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 $60.71   13.307%   $68.7887   $68.79   $68.80   $68.80  
  Purchase #2 $190.58   11.167%   $211.8621   $211.86   $211.85   $211.90  
  Purchase #3 $172.38   12.682%   $194.2412   $194.24   $194.25   $194.20  
  Purchase #4 $131.25   7.873%   $141.5833   $141.58   $141.60   $141.60  
  Purchase #5 $165.26   9.148%   $180.378   $180.38   $180.40   $180.40  
  Purchase #6 $215.44   10.152%   $237.3115   $237.31   $237.30   $237.30  
  Purchase #7 $200.87   9.822%   $220.5995   $220.60   $220.60   $220.60  
  7 purchase totals = $1,136.49       $1,254.7643   $1,254.76   $1,254.80   $1,254.80