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 $219.32   11.278%   $244.0549   $244.05   $244.05   $244.10  
  Purchase #2 $61.89   4.552%   $64.7072   $64.71   $64.70   $64.70  
  Purchase #3 $48.51   9.767%   $53.248   $53.25   $53.25   $53.20  
  Purchase #4 $152.92   7.135%   $163.8308   $163.83   $163.85   $163.80  
  Purchase #5 $54.30   11.672%   $60.6379   $60.64   $60.65   $60.60  
  Purchase #6 $196.67   6.803%   $210.0495   $210.05   $210.05   $210.00  
  Purchase #7 $71.51   4.684%   $74.8595   $74.86   $74.85   $74.90  
  7 purchase totals = $805.12       $871.3878   $871.39   $871.40   $871.30