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 $194.57   5.440%   $205.1546   $205.15   $205.15   $205.20  
  Purchase #2 $13.91   6.761%   $14.8505   $14.85   $14.85   $14.90  
  Purchase #3 $225.59   10.644%   $249.6018   $249.60   $249.60   $249.60  
  Purchase #4 $197.37   13.170%   $223.3636   $223.36   $223.35   $223.40  
  Purchase #5 $50.68   10.174%   $55.8362   $55.84   $55.85   $55.80  
  Purchase #6 $234.54   9.871%   $257.6914   $257.69   $257.70   $257.70  
  Purchase #7 $122.67   10.284%   $135.2854   $135.29   $135.30   $135.30  
  7 purchase totals = $1,039.33       $1,141.7835   $1,141.78   $1,141.80   $1,141.90