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 $119.35   6.607%   $127.2355   $127.24   $127.25   $127.20  
  Purchase #2 $233.49   13.143%   $264.1776   $264.18   $264.20   $264.20  
  Purchase #3 $202.92   12.633%   $228.5549   $228.55   $228.55   $228.60  
  Purchase #4 $176.64   3.855%   $183.4495   $183.45   $183.45   $183.40  
  Purchase #5 $91.64   13.854%   $104.3358   $104.34   $104.35   $104.30  
  Purchase #6 $147.28   4.515%   $153.9297   $153.93   $153.95   $153.90  
  Purchase #7 $20.39   4.339%   $21.2747   $21.27   $21.25   $21.30  
  7 purchase totals = $991.71       $1,082.9577   $1,082.96   $1,083.00   $1,082.90