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 $234.37   13.153%   $265.1967   $265.20   $265.20   $265.20  
  Purchase #2 $35.82   6.147%   $38.0219   $38.02   $38.00   $38.00  
  Purchase #3 $189.51   5.179%   $199.3247   $199.32   $199.30   $199.30  
  Purchase #4 $88.66   4.686%   $92.8146   $92.81   $92.80   $92.80  
  Purchase #5 $178.29   6.763%   $190.3478   $190.35   $190.35   $190.30  
  Purchase #6 $245.50   3.328%   $253.6702   $253.67   $253.65   $253.70  
  Purchase #7 $227.69   12.623%   $256.4313   $256.43   $256.45   $256.40  
  7 purchase totals = $1,199.84       $1,295.8072   $1,295.80   $1,295.75   $1,295.70