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 $106.26   13.667%   $120.7826   $120.78   $120.80   $120.80  
  Purchase #2 $112.54   4.533%   $117.6414   $117.64   $117.65   $117.60  
  Purchase #3 $197.62   6.461%   $210.3882   $210.39   $210.40   $210.40  
  Purchase #4 $154.74   4.113%   $161.1045   $161.10   $161.10   $161.10  
  Purchase #5 $126.92   11.291%   $141.2505   $141.25   $141.25   $141.30  
  Purchase #6 $209.84   10.872%   $232.6538   $232.65   $232.65   $232.70  
  Purchase #7 $127.63   4.206%   $132.9981   $133.00   $133.00   $133.00  
  7 purchase totals = $1,035.55       $1,116.8191   $1,116.81   $1,116.85   $1,116.90