Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.45   12.773%   $246.3526   $246.35   $246.35   $246.40  
  Purchase #2 $201.49   10.490%   $222.6263   $222.63   $222.65   $222.60  
  Purchase #3 $190.49   7.665%   $205.0911   $205.09   $205.10   $205.10  
  Purchase #4 $136.85   12.283%   $153.6593   $153.66   $153.65   $153.70  
  Purchase #5 $151.71   13.425%   $172.0771   $172.08   $172.10   $172.10  
  Purchase #6 $189.27   11.792%   $211.5887   $211.59   $211.60   $211.60  
  Purchase #7 $84.90   13.413%   $96.2876   $96.29   $96.30   $96.30  
  7 purchase totals = $1,173.16       $1,307.6827   $1,307.69   $1,307.75   $1,307.80