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 $14.73   5.395%   $15.5247   $15.52   $15.50   $15.50  
  Purchase #2 $202.67   6.426%   $215.6936   $215.69   $215.70   $215.70  
  Purchase #3 $231.85   8.577%   $251.7358   $251.74   $251.75   $251.70  
  Purchase #4 $56.92   10.203%   $62.7275   $62.73   $62.75   $62.70  
  Purchase #5 $222.89   5.674%   $235.5368   $235.54   $235.55   $235.50  
  Purchase #6 $34.27   11.873%   $38.3389   $38.34   $38.35   $38.30  
  Purchase #7 $222.56   6.561%   $237.1622   $237.16   $237.15   $237.20  
  7 purchase totals = $985.89       $1,056.7195   $1,056.72   $1,056.75   $1,056.60