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 $211.47   3.354%   $218.5627   $218.56   $218.55   $218.60  
  Purchase #2 $219.88   7.293%   $235.9158   $235.92   $235.90   $235.90  
  Purchase #3 $125.75   7.649%   $135.3686   $135.37   $135.35   $135.40  
  Purchase #4 $176.35   12.119%   $197.7219   $197.72   $197.70   $197.70  
  Purchase #5 $69.82   5.580%   $73.716   $73.72   $73.70   $73.70  
  Purchase #6 $159.94   8.764%   $173.9571   $173.96   $173.95   $174.00  
  Purchase #7 $220.67   5.215%   $232.1779   $232.18   $232.20   $232.20  
  7 purchase totals = $1,183.88       $1,267.4200   $1,267.43   $1,267.35   $1,267.50