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 $228.67   6.705%   $244.0023   $244.00   $244.00   $244.00  
  Purchase #2 $94.99   13.803%   $108.1015   $108.10   $108.10   $108.10  
  Purchase #3 $21.92   13.236%   $24.8213   $24.82   $24.80   $24.80  
  Purchase #4 $148.32   11.144%   $164.8488   $164.85   $164.85   $164.80  
  Purchase #5 $155.84   5.557%   $164.5   $164.50   $164.50   $164.50  
  Purchase #6 $102.39   6.351%   $108.8928   $108.89   $108.90   $108.90  
  Purchase #7 $199.68   11.116%   $221.8764   $221.88   $221.90   $221.90  
  7 purchase totals = $951.81       $1,037.0431   $1,037.04   $1,037.05   $1,037.00