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 $206.98   13.189%   $234.2786   $234.28   $234.30   $234.30  
  Purchase #2 $194.63   6.342%   $206.9734   $206.97   $206.95   $207.00  
  Purchase #3 $202.90   11.772%   $226.7854   $226.79   $226.80   $226.80  
  Purchase #4 $200.35   6.704%   $213.7815   $213.78   $213.80   $213.80  
  Purchase #5 $220.84   9.482%   $241.78   $241.78   $241.80   $241.80  
  Purchase #6 $115.34   7.237%   $123.6872   $123.69   $123.70   $123.70  
  Purchase #7 $110.28   7.742%   $118.8179   $118.82   $118.80   $118.80  
  7 purchase totals = $1,251.32       $1,366.1040   $1,366.11   $1,366.15   $1,366.20