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 $44.68   8.643%   $48.5417   $48.54   $48.55   $48.50  
  Purchase #2 $29.59   5.855%   $31.3225   $31.32   $31.30   $31.30  
  Purchase #3 $191.31   8.141%   $206.8845   $206.88   $206.90   $206.90  
  Purchase #4 $194.72   4.103%   $202.7094   $202.71   $202.70   $202.70  
  Purchase #5 $99.92   4.852%   $104.7681   $104.77   $104.75   $104.80  
  Purchase #6 $237.80   8.403%   $257.7823   $257.78   $257.80   $257.80  
  Purchase #7 $189.45   11.263%   $210.7878   $210.79   $210.80   $210.80  
  7 purchase totals = $987.47       $1,062.7963   $1,062.79   $1,062.80   $1,062.80