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 $78.69   5.454%   $82.9818   $82.98   $83.00   $83.00  
  Purchase #2 $191.41   6.510%   $203.8708   $203.87   $203.85   $203.90  
  Purchase #3 $47.56   3.499%   $49.2241   $49.22   $49.20   $49.20  
  Purchase #4 $103.78   4.600%   $108.5539   $108.55   $108.55   $108.60  
  Purchase #5 $36.72   6.660%   $39.1656   $39.17   $39.15   $39.20  
  Purchase #6 $246.97   11.205%   $274.643   $274.64   $274.65   $274.60  
  Purchase #7 $16.54   11.799%   $18.4916   $18.49   $18.50   $18.50  
  7 purchase totals = $721.67       $776.9308   $776.92   $776.90   $777.00