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 $55.33   7.299%   $59.3685   $59.37   $59.35   $59.40  
  Purchase #2 $164.54   6.604%   $175.4062   $175.41   $175.40   $175.40  
  Purchase #3 $222.34   4.811%   $233.0368   $233.04   $233.05   $233.00  
  Purchase #4 $152.77   8.677%   $166.0259   $166.03   $166.05   $166.00  
  Purchase #5 $153.86   4.732%   $161.1407   $161.14   $161.15   $161.10  
  Purchase #6 $60.78   8.491%   $65.9408   $65.94   $65.95   $65.90  
  Purchase #7 $165.46   6.502%   $176.2182   $176.22   $176.20   $176.20  
  7 purchase totals = $975.08       $1,037.1371   $1,037.15   $1,037.15   $1,037.00