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 $51.38   3.132%   $52.9892   $52.99   $53.00   $53.00  
  Purchase #2 $220.44   7.556%   $237.0964   $237.10   $237.10   $237.10  
  Purchase #3 $170.44   7.734%   $183.6218   $183.62   $183.60   $183.60  
  Purchase #4 $59.65   5.675%   $63.0351   $63.04   $63.05   $63.00  
  Purchase #5 $123.52   3.626%   $127.9988   $128.00   $128.00   $128.00  
  Purchase #6 $111.51   10.800%   $123.5531   $123.55   $123.55   $123.60  
  Purchase #7 $144.50   7.501%   $155.3389   $155.34   $155.35   $155.30  
  7 purchase totals = $881.44       $943.6333   $943.64   $943.65   $943.60