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 $85.60   10.377%   $94.4827   $94.48   $94.50   $94.50  
  Purchase #2 $229.81   9.461%   $251.5523   $251.55   $251.55   $251.60  
  Purchase #3 $74.97   10.476%   $82.8239   $82.82   $82.80   $82.80  
  Purchase #4 $126.48   3.435%   $130.8246   $130.82   $130.80   $130.80  
  Purchase #5 $16.52   7.281%   $17.7228   $17.72   $17.70   $17.70  
  Purchase #6 $197.32   13.248%   $223.461   $223.46   $223.45   $223.50  
  Purchase #7 $112.54   5.704%   $118.9593   $118.96   $118.95   $119.00  
  7 purchase totals = $843.24       $919.8266   $919.81   $919.75   $919.90