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 $107.65   6.566%   $114.7183   $114.72   $114.70   $114.70  
  Purchase #2 $231.70   11.171%   $257.5832   $257.58   $257.60   $257.60  
  Purchase #3 $134.45   6.575%   $143.2901   $143.29   $143.30   $143.30  
  Purchase #4 $236.98   7.482%   $254.7108   $254.71   $254.70   $254.70  
  Purchase #5 $215.92   6.650%   $230.2787   $230.28   $230.30   $230.30  
  Purchase #6 $59.56   3.251%   $61.4963   $61.50   $61.50   $61.50  
  Purchase #7 $29.30   7.722%   $31.5625   $31.56   $31.55   $31.60  
  7 purchase totals = $1,015.56       $1,093.6399   $1,093.64   $1,093.65   $1,093.70