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 $203.97   5.401%   $214.9864   $214.99   $215.00   $215.00  
  Purchase #2 $214.70   5.570%   $226.6588   $226.66   $226.65   $226.70  
  Purchase #3 $81.54   13.746%   $92.7485   $92.75   $92.75   $92.70  
  Purchase #4 $113.34   5.183%   $119.2144   $119.21   $119.20   $119.20  
  Purchase #5 $86.54   12.658%   $97.4942   $97.49   $97.50   $97.50  
  Purchase #6 $50.66   13.200%   $57.3471   $57.35   $57.35   $57.30  
  Purchase #7 $242.73   3.586%   $251.4343   $251.43   $251.45   $251.40  
  7 purchase totals = $993.48       $1,059.8837   $1,059.88   $1,059.90   $1,059.80