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 $113.29   11.495%   $126.3127   $126.31   $126.30   $126.30  
  Purchase #2 $17.62   9.400%   $19.2763   $19.28   $19.30   $19.30  
  Purchase #3 $85.56   8.717%   $93.0183   $93.02   $93.00   $93.00  
  Purchase #4 $241.78   9.769%   $265.3995   $265.40   $265.40   $265.40  
  Purchase #5 $204.25   8.299%   $221.2007   $221.20   $221.20   $221.20  
  Purchase #6 $125.45   12.363%   $140.9594   $140.96   $140.95   $141.00  
  Purchase #7 $69.51   6.846%   $74.2687   $74.27   $74.25   $74.30  
  7 purchase totals = $857.46       $940.4356   $940.44   $940.40   $940.50