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 $71.97   11.830%   $80.4841   $80.48   $80.50   $80.50  
  Purchase #2 $107.78   10.421%   $119.0118   $119.01   $119.00   $119.00  
  Purchase #3 $25.55   8.183%   $27.6408   $27.64   $27.65   $27.60  
  Purchase #4 $95.55   13.299%   $108.2572   $108.26   $108.25   $108.30  
  Purchase #5 $178.27   12.456%   $200.4753   $200.48   $200.50   $200.50  
  Purchase #6 $203.91   8.317%   $220.8692   $220.87   $220.85   $220.90  
  Purchase #7 $165.66   5.790%   $175.2517   $175.25   $175.25   $175.30  
  7 purchase totals = $848.69       $931.9901   $931.99   $932.00   $932.10