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 $107.88   10.326%   $119.0197   $119.02   $119.00   $119.00  
  Purchase #2 $66.70   10.750%   $73.8703   $73.87   $73.85   $73.90  
  Purchase #3 $37.36   10.181%   $41.1636   $41.16   $41.15   $41.20  
  Purchase #4 $46.29   6.538%   $49.3164   $49.32   $49.30   $49.30  
  Purchase #5 $49.30   13.816%   $56.1113   $56.11   $56.10   $56.10  
  Purchase #6 $83.61   12.775%   $94.2912   $94.29   $94.30   $94.30  
  Purchase #7 $234.55   10.813%   $259.9119   $259.91   $259.90   $259.90  
  7 purchase totals = $625.69       $693.6844   $693.68   $693.60   $693.70