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 $7.87   6.161%   $8.3549   $8.35   $8.35   $8.40  
  Purchase #2 $32.97   10.608%   $36.4675   $36.47   $36.45   $36.50  
  Purchase #3 $67.47   13.533%   $76.6007   $76.60   $76.60   $76.60  
  Purchase #4 $220.53   4.323%   $230.0635   $230.06   $230.05   $230.10  
  Purchase #5 $91.77   8.557%   $99.6228   $99.62   $99.60   $99.60  
  Purchase #6 $225.44   4.232%   $234.9806   $234.98   $235.00   $235.00  
  Purchase #7 $69.75   5.783%   $73.7836   $73.78   $73.80   $73.80  
  7 purchase totals = $715.80       $759.8736   $759.86   $759.85   $760.00