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 $22.93   8.483%   $24.8752   $24.88   $24.90   $24.90  
  Purchase #2 $57.31   12.808%   $64.6503   $64.65   $64.65   $64.70  
  Purchase #3 $77.44   8.390%   $83.9372   $83.94   $83.95   $83.90  
  Purchase #4 $173.47   6.355%   $184.494   $184.49   $184.50   $184.50  
  Purchase #5 $94.66   6.560%   $100.8697   $100.87   $100.85   $100.90  
  Purchase #6 $43.30   12.703%   $48.8004   $48.80   $48.80   $48.80  
  Purchase #7 $14.76   8.441%   $16.0059   $16.01   $16.00   $16.00  
  7 purchase totals = $483.87       $523.6327   $523.64   $523.65   $523.70