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 $57.52   12.186%   $64.5294   $64.53   $64.55   $64.50  
  Purchase #2 $204.48   9.573%   $224.0549   $224.05   $224.05   $224.10  
  Purchase #3 $104.86   12.469%   $117.935   $117.94   $117.95   $117.90  
  Purchase #4 $198.75   4.398%   $207.491   $207.49   $207.50   $207.50  
  Purchase #5 $228.29   13.147%   $258.3033   $258.30   $258.30   $258.30  
  Purchase #6 $26.76   7.203%   $28.6875   $28.69   $28.70   $28.70  
  Purchase #7 $166.53   10.417%   $183.8774   $183.88   $183.90   $183.90  
  7 purchase totals = $987.19       $1,084.8785   $1,084.88   $1,084.95   $1,084.90