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 $71.32   6.192%   $75.7361   $75.74   $75.75   $75.70  
  Purchase #2 $164.88   4.275%   $171.9286   $171.93   $171.95   $171.90  
  Purchase #3 $10.91   3.780%   $11.3224   $11.32   $11.30   $11.30  
  Purchase #4 $150.73   12.535%   $169.624   $169.62   $169.60   $169.60  
  Purchase #5 $195.47   8.532%   $212.1475   $212.15   $212.15   $212.10  
  Purchase #6 $159.31   4.412%   $166.3388   $166.34   $166.35   $166.30  
  Purchase #7 $84.26   4.619%   $88.152   $88.15   $88.15   $88.20  
  7 purchase totals = $836.88       $895.2494   $895.25   $895.25   $895.10