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 $52.88   11.489%   $58.9554   $58.96   $58.95   $59.00  
  Purchase #2 $5.57   10.310%   $6.1443   $6.14   $6.15   $6.10  
  Purchase #3 $196.86   5.157%   $207.0121   $207.01   $207.00   $207.00  
  Purchase #4 $162.48   7.728%   $175.0365   $175.04   $175.05   $175.00  
  Purchase #5 $62.31   5.307%   $65.6168   $65.62   $65.60   $65.60  
  Purchase #6 $131.27   7.165%   $140.6755   $140.68   $140.70   $140.70  
  Purchase #7 $114.87   8.804%   $124.9832   $124.98   $125.00   $125.00  
  7 purchase totals = $726.24       $778.4238   $778.43   $778.45   $778.40