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 $78.63   11.647%   $87.788   $87.79   $87.80   $87.80  
  Purchase #2 $194.97   11.531%   $217.452   $217.45   $217.45   $217.50  
  Purchase #3 $16.55   12.151%   $18.561   $18.56   $18.55   $18.60  
  Purchase #4 $233.41   5.607%   $246.4973   $246.50   $246.50   $246.50  
  Purchase #5 $240.43   3.507%   $248.8619   $248.86   $248.85   $248.90  
  Purchase #6 $102.49   11.472%   $114.2477   $114.25   $114.25   $114.20  
  Purchase #7 $159.80   11.229%   $177.7439   $177.74   $177.75   $177.70  
  7 purchase totals = $1,026.28       $1,111.1518   $1,111.15   $1,111.15   $1,111.20