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 $37.49   8.499%   $40.6763   $40.68   $40.70   $40.70  
  Purchase #2 $95.45   10.828%   $105.7853   $105.79   $105.80   $105.80  
  Purchase #3 $7.73   5.301%   $8.1398   $8.14   $8.15   $8.10  
  Purchase #4 $14.92   4.576%   $15.6027   $15.60   $15.60   $15.60  
  Purchase #5 $8.48   13.386%   $9.6151   $9.62   $9.60   $9.60  
  Purchase #6 $209.58   12.499%   $235.7754   $235.78   $235.80   $235.80  
  Purchase #7 $153.75   13.424%   $174.3894   $174.39   $174.40   $174.40  
  7 purchase totals = $527.40       $589.9840   $590.00   $590.05   $590.00