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 $68.96   11.449%   $76.8552   $76.86   $76.85   $76.90  
  Purchase #2 $230.31   11.165%   $256.0241   $256.02   $256.00   $256.00  
  Purchase #3 $131.88   4.704%   $138.0836   $138.08   $138.10   $138.10  
  Purchase #4 $59.83   13.240%   $67.7515   $67.75   $67.75   $67.80  
  Purchase #5 $95.54   9.279%   $104.4052   $104.41   $104.40   $104.40  
  Purchase #6 $8.47   5.310%   $8.9198   $8.92   $8.90   $8.90  
  Purchase #7 $118.42   6.335%   $125.9219   $125.92   $125.90   $125.90  
  7 purchase totals = $713.41       $777.9613   $777.96   $777.90   $778.00