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 $64.31   8.526%   $69.7931   $69.79   $69.80   $69.80  
  Purchase #2 $229.82   9.512%   $251.6805   $251.68   $251.70   $251.70  
  Purchase #3 $34.28   10.351%   $37.8283   $37.83   $37.85   $37.80  
  Purchase #4 $112.33   4.493%   $117.377   $117.38   $117.40   $117.40  
  Purchase #5 $122.77   13.198%   $138.9732   $138.97   $138.95   $139.00  
  Purchase #6 $191.66   13.763%   $218.0382   $218.04   $218.05   $218.00  
  Purchase #7 $59.26   11.868%   $66.293   $66.29   $66.30   $66.30  
  7 purchase totals = $814.43       $899.9833   $899.98   $900.05   $900.00