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 $63.31   5.593%   $66.8509   $66.85   $66.85   $66.90  
  Purchase #2 $168.65   4.522%   $176.2764   $176.28   $176.30   $176.30  
  Purchase #3 $232.67   13.873%   $264.9483   $264.95   $264.95   $264.90  
  Purchase #4 $184.30   5.589%   $194.6005   $194.60   $194.60   $194.60  
  Purchase #5 $222.99   4.752%   $233.5865   $233.59   $233.60   $233.60  
  Purchase #6 $242.81   11.607%   $270.993   $270.99   $271.00   $271.00  
  Purchase #7 $197.77   10.758%   $219.0461   $219.05   $219.05   $219.00  
  7 purchase totals = $1,312.50       $1,426.3017   $1,426.31   $1,426.35   $1,426.30