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 $48.59   4.439%   $50.7469   $50.75   $50.75   $50.70  
  Purchase #2 $183.58   8.201%   $198.6354   $198.64   $198.65   $198.60  
  Purchase #3 $85.73   9.813%   $94.1427   $94.14   $94.15   $94.10  
  Purchase #4 $20.45   6.485%   $21.7762   $21.78   $21.80   $21.80  
  Purchase #5 $211.96   5.794%   $224.241   $224.24   $224.25   $224.20  
  Purchase #6 $169.39   9.468%   $185.4278   $185.43   $185.45   $185.40  
  Purchase #7 $56.30   7.216%   $60.3626   $60.36   $60.35   $60.40  
  7 purchase totals = $776.00       $835.3326   $835.34   $835.40   $835.20