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 $118.48   5.214%   $124.6575   $124.66   $124.65   $124.70  
  Purchase #2 $209.69   3.814%   $217.6876   $217.69   $217.70   $217.70  
  Purchase #3 $51.75   8.258%   $56.0235   $56.02   $56.00   $56.00  
  Purchase #4 $149.33   7.199%   $160.0803   $160.08   $160.10   $160.10  
  Purchase #5 $224.46   4.777%   $235.1825   $235.18   $235.20   $235.20  
  Purchase #6 $127.35   9.651%   $139.6405   $139.64   $139.65   $139.60  
  Purchase #7 $106.36   12.355%   $119.5008   $119.50   $119.50   $119.50  
  7 purchase totals = $987.42       $1,052.7727   $1,052.77   $1,052.80   $1,052.80