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 $68.31   9.576%   $74.8514   $74.85   $74.85   $74.90  
  Purchase #2 $23.95   5.725%   $25.3211   $25.32   $25.30   $25.30  
  Purchase #3 $120.35   6.167%   $127.772   $127.77   $127.75   $127.80  
  Purchase #4 $180.67   7.146%   $193.5807   $193.58   $193.60   $193.60  
  Purchase #5 $242.70   5.843%   $256.881   $256.88   $256.90   $256.90  
  Purchase #6 $150.52   9.154%   $164.2986   $164.30   $164.30   $164.30  
  Purchase #7 $73.63   8.796%   $80.1065   $80.11   $80.10   $80.10  
  7 purchase totals = $860.13       $922.8113   $922.81   $922.80   $922.90