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 $100.87   5.399%   $106.316   $106.32   $106.30   $106.30  
  Purchase #2 $166.35   6.161%   $176.5988   $176.60   $176.60   $176.60  
  Purchase #3 $63.85   9.365%   $69.8296   $69.83   $69.85   $69.80  
  Purchase #4 $249.29   11.264%   $277.37   $277.37   $277.35   $277.40  
  Purchase #5 $175.73   4.431%   $183.5166   $183.52   $183.50   $183.50  
  Purchase #6 $245.46   12.379%   $275.8455   $275.85   $275.85   $275.80  
  Purchase #7 $125.89   13.775%   $143.2313   $143.23   $143.25   $143.20  
  7 purchase totals = $1,127.44       $1,232.7078   $1,232.72   $1,232.70   $1,232.60