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 $111.82   5.281%   $117.7252   $117.73   $117.75   $117.70  
  Purchase #2 $245.69   6.205%   $260.9351   $260.94   $260.95   $260.90  
  Purchase #3 $225.69   6.815%   $241.0708   $241.07   $241.05   $241.10  
  Purchase #4 $111.95   6.265%   $118.9637   $118.96   $118.95   $119.00  
  Purchase #5 $48.58   6.327%   $51.6537   $51.65   $51.65   $51.70  
  Purchase #6 $70.35   5.786%   $74.4205   $74.42   $74.40   $74.40  
  Purchase #7 $165.61   9.855%   $181.9309   $181.93   $181.95   $181.90  
  7 purchase totals = $979.69       $1,046.6999   $1,046.70   $1,046.70   $1,046.70