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 $194.38   12.173%   $218.0419   $218.04   $218.05   $218.00  
  Purchase #2 $182.64   9.248%   $199.5305   $199.53   $199.55   $199.50  
  Purchase #3 $71.82   8.134%   $77.6618   $77.66   $77.65   $77.70  
  Purchase #4 $34.97   7.446%   $37.5739   $37.57   $37.55   $37.60  
  Purchase #5 $33.59   9.732%   $36.859   $36.86   $36.85   $36.90  
  Purchase #6 $72.56   10.357%   $80.075   $80.08   $80.10   $80.10  
  Purchase #7 $105.73   4.211%   $110.1823   $110.18   $110.20   $110.20  
  7 purchase totals = $695.69       $759.9244   $759.92   $759.95   $760.00