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 $176.59   12.834%   $199.2536   $199.25   $199.25   $199.30  
  Purchase #2 $57.69   13.479%   $65.466   $65.47   $65.45   $65.50  
  Purchase #3 $205.62   3.197%   $212.1937   $212.19   $212.20   $212.20  
  Purchase #4 $244.84   7.802%   $263.9424   $263.94   $263.95   $263.90  
  Purchase #5 $247.67   13.162%   $280.2683   $280.27   $280.25   $280.30  
  Purchase #6 $141.50   13.536%   $160.6534   $160.65   $160.65   $160.70  
  Purchase #7 $170.73   10.764%   $189.1074   $189.11   $189.10   $189.10  
  7 purchase totals = $1,244.64       $1,370.8848   $1,370.88   $1,370.85   $1,371.00