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 $67.87   9.241%   $74.1419   $74.14   $74.15   $74.10  
  Purchase #2 $24.94   4.439%   $26.0471   $26.05   $26.05   $26.00  
  Purchase #3 $81.95   6.578%   $87.3407   $87.34   $87.35   $87.30  
  Purchase #4 $179.89   4.845%   $188.6057   $188.61   $188.60   $188.60  
  Purchase #5 $9.82   5.450%   $10.3552   $10.36   $10.35   $10.40  
  Purchase #6 $84.29   13.680%   $95.8209   $95.82   $95.80   $95.80  
  Purchase #7 $45.32   12.642%   $51.0494   $51.05   $51.05   $51.00  
  7 purchase totals = $494.08       $533.3609   $533.37   $533.35   $533.20