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 $149.80   12.456%   $168.4591   $168.46   $168.45   $168.50  
  Purchase #2 $211.91   13.406%   $240.3187   $240.32   $240.30   $240.30  
  Purchase #3 $164.72   6.465%   $175.3691   $175.37   $175.35   $175.40  
  Purchase #4 $101.69   8.325%   $110.1557   $110.16   $110.15   $110.20  
  Purchase #5 $58.42   13.505%   $66.3096   $66.31   $66.30   $66.30  
  Purchase #6 $217.26   9.646%   $238.2169   $238.22   $238.20   $238.20  
  Purchase #7 $26.25   4.594%   $27.4559   $27.46   $27.45   $27.50  
  7 purchase totals = $930.05       $1,026.2850   $1,026.30   $1,026.20   $1,026.40