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 $130.91   5.684%   $138.3509   $138.35   $138.35   $138.40  
  Purchase #2 $234.81   10.473%   $259.4017   $259.40   $259.40   $259.40  
  Purchase #3 $69.40   5.292%   $73.0726   $73.07   $73.05   $73.10  
  Purchase #4 $196.27   4.477%   $205.057   $205.06   $205.05   $205.10  
  Purchase #5 $62.43   3.428%   $64.5701   $64.57   $64.55   $64.60  
  Purchase #6 $153.92   6.867%   $164.4897   $164.49   $164.50   $164.50  
  Purchase #7 $146.35   6.362%   $155.6608   $155.66   $155.65   $155.70  
  7 purchase totals = $994.09       $1,060.6028   $1,060.60   $1,060.55   $1,060.80