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 $92.67   11.839%   $103.6412   $103.64   $103.65   $103.60  
  Purchase #2 $178.85   12.141%   $200.5642   $200.56   $200.55   $200.60  
  Purchase #3 $204.77   6.374%   $217.822   $217.82   $217.80   $217.80  
  Purchase #4 $178.57   13.631%   $202.9109   $202.91   $202.90   $202.90  
  Purchase #5 $181.69   13.146%   $205.575   $205.58   $205.60   $205.60  
  Purchase #6 $57.61   12.393%   $64.7496   $64.75   $64.75   $64.70  
  Purchase #7 $188.59   12.119%   $211.4452   $211.45   $211.45   $211.40  
  7 purchase totals = $1,082.75       $1,206.7081   $1,206.71   $1,206.70   $1,206.60