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 $42.79   13.407%   $48.5269   $48.53   $48.55   $48.50  
  Purchase #2 $116.79   8.598%   $126.8316   $126.83   $126.85   $126.80  
  Purchase #3 $229.86   7.807%   $247.8052   $247.81   $247.80   $247.80  
  Purchase #4 $140.72   12.753%   $158.666   $158.67   $158.65   $158.70  
  Purchase #5 $207.97   10.141%   $229.0602   $229.06   $229.05   $229.10  
  Purchase #6 $226.31   8.773%   $246.1642   $246.16   $246.15   $246.20  
  Purchase #7 $61.86   12.625%   $69.6698   $69.67   $69.65   $69.70  
  7 purchase totals = $1,026.30       $1,126.7239   $1,126.73   $1,126.70   $1,126.80