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 $217.94   7.325%   $233.9041   $233.90   $233.90   $233.90  
  Purchase #2 $12.86   11.277%   $14.3102   $14.31   $14.30   $14.30  
  Purchase #3 $58.93   7.176%   $63.1588   $63.16   $63.15   $63.20  
  Purchase #4 $229.82   4.397%   $239.9252   $239.93   $239.95   $239.90  
  Purchase #5 $88.32   6.219%   $93.8126   $93.81   $93.80   $93.80  
  Purchase #6 $184.54   13.654%   $209.7371   $209.74   $209.75   $209.70  
  Purchase #7 $158.25   4.143%   $164.8063   $164.81   $164.80   $164.80  
  7 purchase totals = $950.66       $1,019.6543   $1,019.66   $1,019.65   $1,019.60