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 $154.89   8.227%   $167.6328   $167.63   $167.65   $167.60  
  Purchase #2 $220.36   9.107%   $240.4282   $240.43   $240.45   $240.40  
  Purchase #3 $23.45   3.432%   $24.2548   $24.25   $24.25   $24.30  
  Purchase #4 $63.33   4.165%   $65.9677   $65.97   $65.95   $66.00  
  Purchase #5 $55.54   9.490%   $60.8107   $60.81   $60.80   $60.80  
  Purchase #6 $96.34   10.429%   $106.3873   $106.39   $106.40   $106.40  
  Purchase #7 $110.97   7.840%   $119.67   $119.67   $119.65   $119.70  
  7 purchase totals = $724.88       $785.1515   $785.15   $785.15   $785.20