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 $207.35   8.593%   $225.1676   $225.17   $225.15   $225.20  
  Purchase #2 $155.60   11.544%   $173.5625   $173.56   $173.55   $173.60  
  Purchase #3 $243.29   13.444%   $275.9979   $276.00   $276.00   $276.00  
  Purchase #4 $243.43   8.261%   $263.5398   $263.54   $263.55   $263.50  
  Purchase #5 $54.31   9.459%   $59.4472   $59.45   $59.45   $59.40  
  Purchase #6 $102.78   6.467%   $109.4268   $109.43   $109.45   $109.40  
  Purchase #7 $149.99   13.287%   $169.9192   $169.92   $169.90   $169.90  
  7 purchase totals = $1,156.75       $1,277.0610   $1,277.07   $1,277.05   $1,277.00