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 $94.28   13.132%   $106.6608   $106.66   $106.65   $106.70  
  Purchase #2 $97.96   3.828%   $101.7099   $101.71   $101.70   $101.70  
  Purchase #3 $150.90   7.138%   $161.6712   $161.67   $161.65   $161.70  
  Purchase #4 $235.35   4.432%   $245.7807   $245.78   $245.80   $245.80  
  Purchase #5 $206.78   9.460%   $226.3414   $226.34   $226.35   $226.30  
  Purchase #6 $32.25   11.229%   $35.8714   $35.87   $35.85   $35.90  
  Purchase #7 $111.54   11.374%   $124.2266   $124.23   $124.25   $124.20  
  7 purchase totals = $929.06       $1,002.2620   $1,002.26   $1,002.25   $1,002.30