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 $214.58   10.809%   $237.774   $237.77   $237.75   $237.80  
  Purchase #2 $168.91   8.346%   $183.0072   $183.01   $183.00   $183.00  
  Purchase #3 $31.61   8.448%   $34.2804   $34.28   $34.30   $34.30  
  Purchase #4 $250.97   5.577%   $264.9666   $264.97   $264.95   $265.00  
  Purchase #5 $179.72   13.763%   $204.4549   $204.45   $204.45   $204.50  
  Purchase #6 $6.94   3.447%   $7.1792   $7.18   $7.20   $7.20  
  Purchase #7 $26.69   9.478%   $29.2197   $29.22   $29.20   $29.20  
  7 purchase totals = $879.42       $960.8820   $960.88   $960.85   $961.00