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 $32.77   6.348%   $34.8502   $34.85   $34.85   $34.90  
  Purchase #2 $241.62   9.574%   $264.7527   $264.75   $264.75   $264.80  
  Purchase #3 $122.75   4.414%   $128.1682   $128.17   $128.15   $128.20  
  Purchase #4 $169.34   12.668%   $190.792   $190.79   $190.80   $190.80  
  Purchase #5 $241.37   9.760%   $264.9277   $264.93   $264.95   $264.90  
  Purchase #6 $59.26   10.518%   $65.493   $65.49   $65.50   $65.50  
  Purchase #7 $233.40   6.779%   $249.2222   $249.22   $249.20   $249.20  
  7 purchase totals = $1,100.51       $1,198.2060   $1,198.20   $1,198.20   $1,198.30