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 $212.85   8.332%   $230.5847   $230.58   $230.60   $230.60  
  Purchase #2 $205.36   6.272%   $218.2402   $218.24   $218.25   $218.20  
  Purchase #3 $98.63   12.405%   $110.8651   $110.87   $110.85   $110.90  
  Purchase #4 $43.95   5.234%   $46.2503   $46.25   $46.25   $46.30  
  Purchase #5 $125.61   5.281%   $132.2435   $132.24   $132.25   $132.20  
  Purchase #6 $61.72   11.862%   $69.0412   $69.04   $69.05   $69.00  
  Purchase #7 $212.86   13.638%   $241.8898   $241.89   $241.90   $241.90  
  7 purchase totals = $960.98       $1,049.1148   $1,049.11   $1,049.15   $1,049.10