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 $69.44   11.294%   $77.2826   $77.28   $77.30   $77.30  
  Purchase #2 $131.82   6.687%   $140.6348   $140.63   $140.65   $140.60  
  Purchase #3 $122.56   5.582%   $129.4013   $129.40   $129.40   $129.40  
  Purchase #4 $85.81   6.759%   $91.6099   $91.61   $91.60   $91.60  
  Purchase #5 $18.58   12.658%   $20.9319   $20.93   $20.95   $20.90  
  Purchase #6 $178.33   3.590%   $184.732   $184.73   $184.75   $184.70  
  Purchase #7 $187.80   5.541%   $198.206   $198.21   $198.20   $198.20  
  7 purchase totals = $794.34       $842.7985   $842.79   $842.85   $842.70