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 $136.53   7.803%   $147.1834   $147.18   $147.20   $147.20  
  Purchase #2 $247.42   13.799%   $281.5615   $281.56   $281.55   $281.60  
  Purchase #3 $110.41   8.582%   $119.8854   $119.89   $119.90   $119.90  
  Purchase #4 $29.48   10.464%   $32.5648   $32.56   $32.55   $32.60  
  Purchase #5 $116.50   13.411%   $132.1238   $132.12   $132.10   $132.10  
  Purchase #6 $39.78   9.749%   $43.6582   $43.66   $43.65   $43.70  
  Purchase #7 $215.37   13.396%   $244.221   $244.22   $244.20   $244.20  
  7 purchase totals = $895.49       $1,001.1981   $1,001.19   $1,001.15   $1,001.30