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 $113.32   13.820%   $128.9808   $128.98   $129.00   $129.00  
  Purchase #2 $70.95   7.611%   $76.35   $76.35   $76.35   $76.40  
  Purchase #3 $153.69   8.844%   $167.2823   $167.28   $167.30   $167.30  
  Purchase #4 $175.67   5.785%   $185.8325   $185.83   $185.85   $185.80  
  Purchase #5 $106.46   11.236%   $118.4218   $118.42   $118.40   $118.40  
  Purchase #6 $66.48   3.658%   $68.9118   $68.91   $68.90   $68.90  
  Purchase #7 $138.92   12.313%   $156.0252   $156.03   $156.05   $156.00  
  7 purchase totals = $825.49       $901.8044   $901.80   $901.85   $901.80