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 $212.79   8.671%   $231.241   $231.24   $231.25   $231.20  
  Purchase #2 $110.65   13.735%   $125.8478   $125.85   $125.85   $125.80  
  Purchase #3 $114.57   12.348%   $128.7171   $128.72   $128.70   $128.70  
  Purchase #4 $187.78   8.262%   $203.2944   $203.29   $203.30   $203.30  
  Purchase #5 $124.41   12.287%   $139.6963   $139.70   $139.70   $139.70  
  Purchase #6 $145.32   11.132%   $161.497   $161.50   $161.50   $161.50  
  Purchase #7 $29.93   9.363%   $32.7323   $32.73   $32.75   $32.70  
  7 purchase totals = $925.45       $1,023.0259   $1,023.03   $1,023.05   $1,022.90