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 $234.96   11.510%   $262.0039   $262.00   $262.00   $262.00  
  Purchase #2 $82.28   13.220%   $93.1574   $93.16   $93.15   $93.20  
  Purchase #3 $108.43   8.583%   $117.7365   $117.74   $117.75   $117.70  
  Purchase #4 $146.39   3.543%   $151.5766   $151.58   $151.60   $151.60  
  Purchase #5 $192.35   10.320%   $212.2005   $212.20   $212.20   $212.20  
  Purchase #6 $189.59   13.800%   $215.7534   $215.75   $215.75   $215.80  
  Purchase #7 $16.93   5.282%   $17.8242   $17.82   $17.80   $17.80  
  7 purchase totals = $970.93       $1,070.2525   $1,070.25   $1,070.25   $1,070.30