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 $110.95   6.378%   $118.0264   $118.03   $118.05   $118.00  
  Purchase #2 $68.99   12.816%   $77.8318   $77.83   $77.85   $77.80  
  Purchase #3 $97.87   11.281%   $108.9107   $108.91   $108.90   $108.90  
  Purchase #4 $130.59   3.657%   $135.3657   $135.37   $135.35   $135.40  
  Purchase #5 $51.82   8.645%   $56.2998   $56.30   $56.30   $56.30  
  Purchase #6 $80.53   13.287%   $91.23   $91.23   $91.25   $91.20  
  Purchase #7 $24.97   12.234%   $28.0248   $28.02   $28.00   $28.00  
  7 purchase totals = $565.72       $615.6892   $615.69   $615.70   $615.60