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 $42.67   8.509%   $46.3008   $46.30   $46.30   $46.30  
  Purchase #2 $228.31   11.759%   $255.157   $255.16   $255.15   $255.20  
  Purchase #3 $90.57   4.596%   $94.7326   $94.73   $94.75   $94.70  
  Purchase #4 $173.59   8.205%   $187.8331   $187.83   $187.85   $187.80  
  Purchase #5 $164.56   10.514%   $181.8618   $181.86   $181.85   $181.90  
  Purchase #6 $225.75   12.299%   $253.515   $253.52   $253.50   $253.50  
  Purchase #7 $98.48   6.244%   $104.6291   $104.63   $104.65   $104.60  
  7 purchase totals = $1,023.93       $1,124.0294   $1,124.03   $1,124.05   $1,124.00