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 $125.55   7.105%   $134.4703   $134.47   $134.45   $134.50  
  Purchase #2 $172.42   12.414%   $193.8242   $193.82   $193.80   $193.80  
  Purchase #3 $157.99   7.861%   $170.4096   $170.41   $170.40   $170.40  
  Purchase #4 $32.53   12.720%   $36.6678   $36.67   $36.65   $36.70  
  Purchase #5 $244.67   8.801%   $266.2034   $266.20   $266.20   $266.20  
  Purchase #6 $34.41   7.450%   $36.9735   $36.97   $36.95   $37.00  
  Purchase #7 $41.25   13.860%   $46.9673   $46.97   $46.95   $47.00  
  7 purchase totals = $808.82       $885.5161   $885.51   $885.40   $885.60