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 $61.92   7.485%   $66.5547   $66.55   $66.55   $66.60  
  Purchase #2 $126.73   7.746%   $136.5465   $136.55   $136.55   $136.50  
  Purchase #3 $20.98   7.291%   $22.5097   $22.51   $22.50   $22.50  
  Purchase #4 $199.39   6.306%   $211.9635   $211.96   $211.95   $212.00  
  Purchase #5 $232.75   9.606%   $255.108   $255.11   $255.10   $255.10  
  Purchase #6 $197.52   4.108%   $205.6341   $205.63   $205.65   $205.60  
  Purchase #7 $96.82   5.529%   $102.1732   $102.17   $102.15   $102.20  
  7 purchase totals = $936.11       $1,000.4897   $1,000.48   $1,000.45   $1,000.50