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 $169.27   6.120%   $179.6293   $179.63   $179.65   $179.60  
  Purchase #2 $195.53   4.181%   $203.7051   $203.71   $203.70   $203.70  
  Purchase #3 $53.30   7.117%   $57.0934   $57.09   $57.10   $57.10  
  Purchase #4 $118.40   12.127%   $132.7584   $132.76   $132.75   $132.80  
  Purchase #5 $199.99   10.654%   $221.2969   $221.30   $221.30   $221.30  
  Purchase #6 $197.67   13.583%   $224.5195   $224.52   $224.50   $224.50  
  Purchase #7 $85.35   7.202%   $91.4969   $91.50   $91.50   $91.50  
  7 purchase totals = $1,019.51       $1,110.4995   $1,110.51   $1,110.50   $1,110.50