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 $59.50   8.634%   $64.6372   $64.64   $64.65   $64.60  
  Purchase #2 $224.69   11.776%   $251.1495   $251.15   $251.15   $251.10  
  Purchase #3 $149.84   11.213%   $166.6416   $166.64   $166.65   $166.60  
  Purchase #4 $59.27   12.425%   $66.6343   $66.63   $66.65   $66.60  
  Purchase #5 $152.34   12.322%   $171.1113   $171.11   $171.10   $171.10  
  Purchase #6 $202.79   7.463%   $217.9242   $217.92   $217.90   $217.90  
  Purchase #7 $11.58   8.847%   $12.6045   $12.60   $12.60   $12.60  
  7 purchase totals = $860.01       $950.7026   $950.69   $950.70   $950.50