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 $221.41   4.869%   $232.1905   $232.19   $232.20   $232.20  
  Purchase #2 $248.75   3.784%   $258.1627   $258.16   $258.15   $258.20  
  Purchase #3 $248.75   9.288%   $271.8539   $271.85   $271.85   $271.90  
  Purchase #4 $23.28   4.410%   $24.3066   $24.31   $24.30   $24.30  
  Purchase #5 $87.35   10.517%   $96.5366   $96.54   $96.55   $96.50  
  Purchase #6 $243.25   13.300%   $275.6023   $275.60   $275.60   $275.60  
  Purchase #7 $103.34   12.364%   $116.117   $116.12   $116.10   $116.10  
  7 purchase totals = $1,176.13       $1,274.7696   $1,274.77   $1,274.75   $1,274.80