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 $219.93   11.368%   $244.9316   $244.93   $244.95   $244.90  
  Purchase #2 $224.55   4.313%   $234.2348   $234.23   $234.25   $234.20  
  Purchase #3 $163.85   4.395%   $171.0512   $171.05   $171.05   $171.10  
  Purchase #4 $27.73   3.706%   $28.7577   $28.76   $28.75   $28.80  
  Purchase #5 $28.41   12.734%   $32.0277   $32.03   $32.05   $32.00  
  Purchase #6 $5.58   12.681%   $6.2876   $6.29   $6.30   $6.30  
  Purchase #7 $24.35   9.110%   $26.5683   $26.57   $26.55   $26.60  
  7 purchase totals = $694.40       $743.8589   $743.86   $743.90   $743.90