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 $119.43   10.264%   $131.6883   $131.69   $131.70   $131.70  
  Purchase #2 $195.65   4.437%   $204.331   $204.33   $204.35   $204.30  
  Purchase #3 $23.36   8.468%   $25.3381   $25.34   $25.35   $25.30  
  Purchase #4 $204.99   8.801%   $223.0312   $223.03   $223.05   $223.00  
  Purchase #5 $140.39   6.714%   $149.8158   $149.82   $149.80   $149.80  
  Purchase #6 $235.27   3.267%   $242.9563   $242.96   $242.95   $243.00  
  Purchase #7 $17.99   5.403%   $18.962   $18.96   $18.95   $19.00  
  7 purchase totals = $937.08       $996.1227   $996.13   $996.15   $996.10