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 $82.26   6.602%   $87.6908   $87.69   $87.70   $87.70  
  Purchase #2 $211.62   12.794%   $238.6947   $238.69   $238.70   $238.70  
  Purchase #3 $20.59   13.782%   $23.4277   $23.43   $23.45   $23.40  
  Purchase #4 $81.87   5.731%   $86.562   $86.56   $86.55   $86.60  
  Purchase #5 $245.75   9.761%   $269.7377   $269.74   $269.75   $269.70  
  Purchase #6 $94.69   8.578%   $102.8125   $102.81   $102.80   $102.80  
  Purchase #7 $189.26   5.624%   $199.904   $199.90   $199.90   $199.90  
  7 purchase totals = $926.04       $1,008.8294   $1,008.82   $1,008.85   $1,008.80