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 $59.76   3.337%   $61.7542   $61.75   $61.75   $61.80  
  Purchase #2 $237.53   3.177%   $245.0763   $245.08   $245.10   $245.10  
  Purchase #3 $136.75   6.708%   $145.9232   $145.92   $145.90   $145.90  
  Purchase #4 $87.26   6.406%   $92.8499   $92.85   $92.85   $92.80  
  Purchase #5 $90.74   4.607%   $94.9204   $94.92   $94.90   $94.90  
  Purchase #6 $225.80   6.351%   $240.1406   $240.14   $240.15   $240.10  
  Purchase #7 $104.37   12.637%   $117.5592   $117.56   $117.55   $117.60  
  7 purchase totals = $942.21       $998.2238   $998.22   $998.20   $998.20