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 $48.91   12.673%   $55.1084   $55.11   $55.10   $55.10  
  Purchase #2 $216.96   12.156%   $243.3337   $243.33   $243.35   $243.30  
  Purchase #3 $90.40   13.588%   $102.6836   $102.68   $102.70   $102.70  
  Purchase #4 $174.68   13.796%   $198.7789   $198.78   $198.80   $198.80  
  Purchase #5 $116.44   5.555%   $122.9082   $122.91   $122.90   $122.90  
  Purchase #6 $236.50   12.603%   $266.3061   $266.31   $266.30   $266.30  
  Purchase #7 $19.93   13.736%   $22.6676   $22.67   $22.65   $22.70  
  7 purchase totals = $903.82       $1,011.7865   $1,011.79   $1,011.80   $1,011.80