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 $146.93   10.615%   $162.5266   $162.53   $162.55   $162.50  
  Purchase #2 $155.37   10.422%   $171.5627   $171.56   $171.55   $171.60  
  Purchase #3 $24.67   3.858%   $25.6218   $25.62   $25.60   $25.60  
  Purchase #4 $68.81   4.146%   $71.6629   $71.66   $71.65   $71.70  
  Purchase #5 $236.57   3.199%   $244.1379   $244.14   $244.15   $244.10  
  Purchase #6 $220.90   4.552%   $230.9554   $230.96   $230.95   $231.00  
  Purchase #7 $105.62   13.465%   $119.8417   $119.84   $119.85   $119.80  
  7 purchase totals = $958.87       $1,026.3090   $1,026.31   $1,026.30   $1,026.30