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 $218.73   13.476%   $248.2061   $248.21   $248.20   $248.20  
  Purchase #2 $101.45   5.140%   $106.6645   $106.66   $106.65   $106.70  
  Purchase #3 $50.80   12.726%   $57.2648   $57.26   $57.25   $57.30  
  Purchase #4 $211.26   10.435%   $233.305   $233.31   $233.30   $233.30  
  Purchase #5 $136.92   3.224%   $141.3343   $141.33   $141.35   $141.30  
  Purchase #6 $205.30   13.608%   $233.2372   $233.24   $233.25   $233.20  
  Purchase #7 $31.48   8.374%   $34.1161   $34.12   $34.10   $34.10  
  7 purchase totals = $955.94       $1,054.1280   $1,054.13   $1,054.10   $1,054.10