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 $31.25   8.707%   $33.9709   $33.97   $33.95   $34.00  
  Purchase #2 $138.61   9.633%   $151.9623   $151.96   $151.95   $152.00  
  Purchase #3 $85.52   3.423%   $88.4473   $88.45   $88.45   $88.40  
  Purchase #4 $209.40   9.493%   $229.2783   $229.28   $229.30   $229.30  
  Purchase #5 $57.84   6.328%   $61.5001   $61.50   $61.50   $61.50  
  Purchase #6 $205.95   4.739%   $215.71   $215.71   $215.70   $215.70  
  Purchase #7 $183.97   12.595%   $207.141   $207.14   $207.15   $207.10  
  7 purchase totals = $912.54       $988.0099   $988.01   $988.00   $988.00