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 $56.96   3.114%   $58.7337   $58.73   $58.75   $58.70  
  Purchase #2 $64.79   4.114%   $67.4555   $67.46   $67.45   $67.50  
  Purchase #3 $10.62   3.636%   $11.0061   $11.01   $11.00   $11.00  
  Purchase #4 $196.54   4.683%   $205.744   $205.74   $205.75   $205.70  
  Purchase #5 $46.63   6.127%   $49.487   $49.49   $49.50   $49.50  
  Purchase #6 $70.76   6.278%   $75.2023   $75.20   $75.20   $75.20  
  Purchase #7 $5.82   11.373%   $6.4819   $6.48   $6.50   $6.50  
  7 purchase totals = $452.12       $474.1105   $474.11   $474.15   $474.10