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 $29.45   12.143%   $33.0261   $33.03   $33.05   $33.00  
  Purchase #2 $133.77   7.445%   $143.7292   $143.73   $143.75   $143.70  
  Purchase #3 $125.65   11.422%   $140.0017   $140.00   $140.00   $140.00  
  Purchase #4 $195.25   7.102%   $209.1167   $209.12   $209.10   $209.10  
  Purchase #5 $164.50   10.503%   $181.7774   $181.78   $181.80   $181.80  
  Purchase #6 $201.64   10.610%   $223.034   $223.03   $223.05   $223.00  
  Purchase #7 $64.31   13.502%   $72.9931   $72.99   $73.00   $73.00  
  7 purchase totals = $914.57       $1,003.6782   $1,003.68   $1,003.75   $1,003.60