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 $82.64   12.682%   $93.1204   $93.12   $93.10   $93.10  
  Purchase #2 $206.45   13.477%   $234.2733   $234.27   $234.25   $234.30  
  Purchase #3 $82.26   13.362%   $93.2516   $93.25   $93.25   $93.30  
  Purchase #4 $14.74   12.425%   $16.5714   $16.57   $16.55   $16.60  
  Purchase #5 $246.41   8.500%   $267.3549   $267.35   $267.35   $267.40  
  Purchase #6 $38.85   11.516%   $43.324   $43.32   $43.30   $43.30  
  Purchase #7 $8.35   10.260%   $9.2067   $9.21   $9.20   $9.20  
  7 purchase totals = $679.70       $757.1023   $757.09   $757.00   $757.20