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 $189.27   6.723%   $201.9946   $201.99   $202.00   $202.00  
  Purchase #2 $205.45   9.186%   $224.3226   $224.32   $224.30   $224.30  
  Purchase #3 $10.57   3.760%   $10.9674   $10.97   $10.95   $11.00  
  Purchase #4 $167.78   10.704%   $185.7392   $185.74   $185.75   $185.70  
  Purchase #5 $81.25   7.729%   $87.5298   $87.53   $87.55   $87.50  
  Purchase #6 $31.80   6.587%   $33.8947   $33.89   $33.90   $33.90  
  Purchase #7 $20.75   4.152%   $21.6115   $21.61   $21.60   $21.60  
  7 purchase totals = $706.87       $766.0598   $766.05   $766.05   $766.00