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 $61.38   11.701%   $68.5621   $68.56   $68.55   $68.60  
  Purchase #2 $180.73   6.121%   $191.7925   $191.79   $191.80   $191.80  
  Purchase #3 $141.95   12.478%   $159.6625   $159.66   $159.65   $159.70  
  Purchase #4 $68.66   3.336%   $70.9505   $70.95   $70.95   $71.00  
  Purchase #5 $52.42   3.619%   $54.3171   $54.32   $54.30   $54.30  
  Purchase #6 $121.97   4.445%   $127.3916   $127.39   $127.40   $127.40  
  Purchase #7 $194.91   8.709%   $211.8847   $211.88   $211.90   $211.90  
  7 purchase totals = $822.02       $884.5610   $884.55   $884.55   $884.70