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 $209.32   11.734%   $233.8816   $233.88   $233.90   $233.90  
  Purchase #2 $59.62   11.764%   $66.6337   $66.63   $66.65   $66.60  
  Purchase #3 $106.43   10.472%   $117.5753   $117.58   $117.60   $117.60  
  Purchase #4 $25.95   6.373%   $27.6038   $27.60   $27.60   $27.60  
  Purchase #5 $233.84   11.490%   $260.7082   $260.71   $260.70   $260.70  
  Purchase #6 $53.67   6.148%   $56.9696   $56.97   $56.95   $57.00  
  Purchase #7 $214.63   3.508%   $222.1592   $222.16   $222.15   $222.20  
  7 purchase totals = $903.46       $985.5314   $985.53   $985.55   $985.60