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 $144.92   7.339%   $155.5557   $155.56   $155.55   $155.60  
  Purchase #2 $56.48   11.316%   $62.8713   $62.87   $62.85   $62.90  
  Purchase #3 $66.61   13.148%   $75.3679   $75.37   $75.35   $75.40  
  Purchase #4 $52.88   13.294%   $59.9099   $59.91   $59.90   $59.90  
  Purchase #5 $198.92   4.601%   $208.0723   $208.07   $208.05   $208.10  
  Purchase #6 $160.28   5.441%   $169.0008   $169.00   $169.00   $169.00  
  Purchase #7 $246.29   4.772%   $258.043   $258.04   $258.05   $258.00  
  7 purchase totals = $926.38       $988.8209   $988.82   $988.75   $988.90