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 $74.55   8.525%   $80.9054   $80.91   $80.90   $80.90  
  Purchase #2 $85.43   11.161%   $94.9648   $94.96   $94.95   $95.00  
  Purchase #3 $86.96   12.554%   $97.877   $97.88   $97.90   $97.90  
  Purchase #4 $165.91   7.525%   $178.3947   $178.39   $178.40   $178.40  
  Purchase #5 $200.50   12.783%   $226.1299   $226.13   $226.15   $226.10  
  Purchase #6 $97.67   12.842%   $110.2128   $110.21   $110.20   $110.20  
  Purchase #7 $51.63   11.219%   $57.4224   $57.42   $57.40   $57.40  
  7 purchase totals = $762.65       $845.9070   $845.90   $845.90   $845.90