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 $215.33   7.721%   $231.9556   $231.96   $231.95   $232.00  
  Purchase #2 $55.30   8.248%   $59.8611   $59.86   $59.85   $59.90  
  Purchase #3 $72.82   13.273%   $82.4854   $82.49   $82.50   $82.50  
  Purchase #4 $177.29   13.842%   $201.8305   $201.83   $201.85   $201.80  
  Purchase #5 $60.75   12.225%   $68.1767   $68.18   $68.20   $68.20  
  Purchase #6 $6.27   13.299%   $7.1038   $7.10   $7.10   $7.10  
  Purchase #7 $85.90   13.248%   $97.28   $97.28   $97.30   $97.30  
  7 purchase totals = $673.66       $748.6931   $748.70   $748.75   $748.80