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 $223.70   5.108%   $235.1266   $235.13   $235.15   $235.10  
  Purchase #2 $6.95   6.828%   $7.4245   $7.42   $7.40   $7.40  
  Purchase #3 $181.86   9.717%   $199.5313   $199.53   $199.55   $199.50  
  Purchase #4 $19.86   7.400%   $21.3296   $21.33   $21.35   $21.30  
  Purchase #5 $84.90   11.702%   $94.835   $94.84   $94.85   $94.80  
  Purchase #6 $197.54   4.246%   $205.9275   $205.93   $205.95   $205.90  
  Purchase #7 $64.36   6.842%   $68.7635   $68.76   $68.75   $68.80  
  7 purchase totals = $779.17       $832.9380   $832.94   $833.00   $832.80