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 $82.87   11.210%   $92.1597   $92.16   $92.15   $92.20  
  Purchase #2 $223.84   12.512%   $251.8469   $251.85   $251.85   $251.80  
  Purchase #3 $112.78   8.109%   $121.9253   $121.93   $121.95   $121.90  
  Purchase #4 $154.64   12.699%   $174.2777   $174.28   $174.30   $174.30  
  Purchase #5 $67.64   11.397%   $75.3489   $75.35   $75.35   $75.30  
  Purchase #6 $157.25   11.521%   $175.3668   $175.37   $175.35   $175.40  
  Purchase #7 $200.96   13.444%   $227.9771   $227.98   $228.00   $228.00  
  7 purchase totals = $999.98       $1,118.9024   $1,118.92   $1,118.95   $1,118.90