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 $61.64   4.822%   $64.6123   $64.61   $64.60   $64.60  
  Purchase #2 $48.48   13.778%   $55.1596   $55.16   $55.15   $55.20  
  Purchase #3 $188.97   3.292%   $195.1909   $195.19   $195.20   $195.20  
  Purchase #4 $147.73   12.707%   $166.5021   $166.50   $166.50   $166.50  
  Purchase #5 $117.92   5.761%   $124.7134   $124.71   $124.70   $124.70  
  Purchase #6 $80.61   6.422%   $85.7868   $85.79   $85.80   $85.80  
  Purchase #7 $207.67   9.506%   $227.4111   $227.41   $227.40   $227.40  
  7 purchase totals = $853.02       $919.3762   $919.37   $919.35   $919.40