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 $233.27   11.760%   $260.7026   $260.70   $260.70   $260.70  
  Purchase #2 $88.78   9.279%   $97.0179   $97.02   $97.00   $97.00  
  Purchase #3 $94.25   11.111%   $104.7221   $104.72   $104.70   $104.70  
  Purchase #4 $244.27   6.472%   $260.0792   $260.08   $260.10   $260.10  
  Purchase #5 $16.75   4.445%   $17.4945   $17.49   $17.50   $17.50  
  Purchase #6 $202.36   3.521%   $209.4851   $209.49   $209.50   $209.50  
  Purchase #7 $60.92   7.189%   $65.2995   $65.30   $65.30   $65.30  
  7 purchase totals = $940.60       $1,014.8009   $1,014.80   $1,014.80   $1,014.80