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 $200.67   12.634%   $226.0226   $226.02   $226.00   $226.00  
  Purchase #2 $209.53   9.191%   $228.7879   $228.79   $228.80   $228.80  
  Purchase #3 $126.29   11.406%   $140.6946   $140.69   $140.70   $140.70  
  Purchase #4 $23.48   11.446%   $26.1675   $26.17   $26.15   $26.20  
  Purchase #5 $223.40   13.816%   $254.2649   $254.26   $254.25   $254.30  
  Purchase #6 $174.66   4.617%   $182.7241   $182.72   $182.70   $182.70  
  Purchase #7 $133.62   13.369%   $151.4837   $151.48   $151.50   $151.50  
  7 purchase totals = $1,091.65       $1,210.1453   $1,210.13   $1,210.10   $1,210.20