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 $41.39   11.387%   $46.1031   $46.10   $46.10   $46.10  
  Purchase #2 $204.87   7.368%   $219.9648   $219.96   $219.95   $220.00  
  Purchase #3 $26.58   4.874%   $27.8755   $27.88   $27.90   $27.90  
  Purchase #4 $129.89   12.445%   $146.0548   $146.05   $146.05   $146.10  
  Purchase #5 $166.59   13.337%   $188.8081   $188.81   $188.80   $188.80  
  Purchase #6 $243.99   5.150%   $256.5555   $256.56   $256.55   $256.60  
  Purchase #7 $122.99   5.363%   $129.586   $129.59   $129.60   $129.60  
  7 purchase totals = $936.30       $1,014.9478   $1,014.95   $1,014.95   $1,015.10