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 $58.39   4.785%   $61.184   $61.18   $61.20   $61.20  
  Purchase #2 $14.67   13.620%   $16.6681   $16.67   $16.65   $16.70  
  Purchase #3 $123.76   8.555%   $134.3477   $134.35   $134.35   $134.30  
  Purchase #4 $212.56   12.110%   $238.301   $238.30   $238.30   $238.30  
  Purchase #5 $127.71   3.670%   $132.397   $132.40   $132.40   $132.40  
  Purchase #6 $114.51   7.169%   $122.7192   $122.72   $122.70   $122.70  
  Purchase #7 $229.69   6.575%   $244.7921   $244.79   $244.80   $244.80  
  7 purchase totals = $881.29       $950.4091   $950.41   $950.40   $950.40