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 $239.83   12.170%   $269.0173   $269.02   $269.00   $269.00  
  Purchase #2 $93.38   8.128%   $100.9699   $100.97   $100.95   $101.00  
  Purchase #3 $181.65   12.719%   $204.7541   $204.75   $204.75   $204.80  
  Purchase #4 $53.65   10.702%   $59.3916   $59.39   $59.40   $59.40  
  Purchase #5 $71.47   7.820%   $77.059   $77.06   $77.05   $77.10  
  Purchase #6 $129.71   3.752%   $134.5767   $134.58   $134.60   $134.60  
  Purchase #7 $136.38   9.301%   $149.0647   $149.06   $149.05   $149.10  
  7 purchase totals = $906.07       $994.8333   $994.83   $994.80   $995.00