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 $224.61   8.865%   $244.5217   $244.52   $244.50   $244.50  
  Purchase #2 $195.99   8.446%   $212.5433   $212.54   $212.55   $212.50  
  Purchase #3 $32.32   8.143%   $34.9518   $34.95   $34.95   $35.00  
  Purchase #4 $150.36   7.813%   $162.1076   $162.11   $162.10   $162.10  
  Purchase #5 $119.82   9.743%   $131.4941   $131.49   $131.50   $131.50  
  Purchase #6 $215.26   6.131%   $228.4576   $228.46   $228.45   $228.50  
  Purchase #7 $214.97   9.629%   $235.6695   $235.67   $235.65   $235.70  
  7 purchase totals = $1,153.33       $1,249.7456   $1,249.74   $1,249.70   $1,249.80