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 $189.63   10.572%   $209.6777   $209.68   $209.70   $209.70  
  Purchase #2 $42.75   8.423%   $46.3508   $46.35   $46.35   $46.40  
  Purchase #3 $181.42   5.759%   $191.868   $191.87   $191.85   $191.90  
  Purchase #4 $200.35   6.580%   $213.533   $213.53   $213.55   $213.50  
  Purchase #5 $28.49   3.151%   $29.3877   $29.39   $29.40   $29.40  
  Purchase #6 $160.29   5.380%   $168.9136   $168.91   $168.90   $168.90  
  Purchase #7 $126.47   11.265%   $140.7168   $140.72   $140.70   $140.70  
  7 purchase totals = $929.40       $1,000.4476   $1,000.45   $1,000.45   $1,000.50