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 $62.32   6.252%   $66.2162   $66.22   $66.20   $66.20  
  Purchase #2 $22.92   3.257%   $23.6665   $23.67   $23.65   $23.70  
  Purchase #3 $148.54   6.485%   $158.1728   $158.17   $158.15   $158.20  
  Purchase #4 $118.66   5.224%   $124.8588   $124.86   $124.85   $124.90  
  Purchase #5 $181.95   10.528%   $201.1057   $201.11   $201.10   $201.10  
  Purchase #6 $233.41   9.256%   $255.0144   $255.01   $255.00   $255.00  
  Purchase #7 $201.79   8.293%   $218.5244   $218.52   $218.50   $218.50  
  7 purchase totals = $969.59       $1,047.5588   $1,047.56   $1,047.45   $1,047.60