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 $54.84   10.854%   $60.7923   $60.79   $60.80   $60.80  
  Purchase #2 $220.94   9.698%   $242.3668   $242.37   $242.35   $242.40  
  Purchase #3 $63.79   7.314%   $68.4556   $68.46   $68.45   $68.50  
  Purchase #4 $46.70   13.317%   $52.919   $52.92   $52.90   $52.90  
  Purchase #5 $140.86   6.452%   $149.9483   $149.95   $149.95   $149.90  
  Purchase #6 $71.77   5.255%   $75.5415   $75.54   $75.55   $75.50  
  Purchase #7 $196.56   6.844%   $210.0126   $210.01   $210.00   $210.00  
  7 purchase totals = $795.46       $860.0361   $860.04   $860.00   $860.00