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 $97.47   13.718%   $110.8409   $110.84   $110.85   $110.80  
  Purchase #2 $201.41   12.872%   $227.3355   $227.34   $227.35   $227.30  
  Purchase #3 $160.95   5.451%   $169.7234   $169.72   $169.70   $169.70  
  Purchase #4 $9.28   12.691%   $10.4577   $10.46   $10.45   $10.50  
  Purchase #5 $193.49   5.600%   $204.3254   $204.33   $204.35   $204.30  
  Purchase #6 $238.79   4.786%   $250.2185   $250.22   $250.20   $250.20  
  Purchase #7 $170.84   13.293%   $193.5498   $193.55   $193.55   $193.50  
  7 purchase totals = $1,072.23       $1,166.4512   $1,166.46   $1,166.45   $1,166.30