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 $118.95   11.260%   $132.3438   $132.34   $132.35   $132.30  
  Purchase #2 $219.41   9.694%   $240.6796   $240.68   $240.70   $240.70  
  Purchase #3 $163.90   13.618%   $186.2199   $186.22   $186.20   $186.20  
  Purchase #4 $68.81   10.280%   $75.8837   $75.88   $75.90   $75.90  
  Purchase #5 $90.53   13.732%   $102.9616   $102.96   $102.95   $103.00  
  Purchase #6 $25.35   9.201%   $27.6825   $27.68   $27.70   $27.70  
  Purchase #7 $209.81   7.819%   $226.215   $226.22   $226.20   $226.20  
  7 purchase totals = $896.76       $991.9861   $991.98   $992.00   $992.00