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 $32.81   8.514%   $35.6034   $35.60   $35.60   $35.60  
  Purchase #2 $43.99   9.841%   $48.3191   $48.32   $48.30   $48.30  
  Purchase #3 $51.62   11.705%   $57.6621   $57.66   $57.65   $57.70  
  Purchase #4 $117.98   6.150%   $125.2358   $125.24   $125.25   $125.20  
  Purchase #5 $181.90   13.819%   $207.0368   $207.04   $207.05   $207.00  
  Purchase #6 $189.36   11.533%   $211.1989   $211.20   $211.20   $211.20  
  Purchase #7 $85.77   11.776%   $95.8703   $95.87   $95.85   $95.90  
  7 purchase totals = $703.43       $780.9264   $780.93   $780.90   $780.90