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 $221.53   11.193%   $246.3259   $246.33   $246.35   $246.30  
  Purchase #2 $65.37   13.627%   $74.278   $74.28   $74.30   $74.30  
  Purchase #3 $228.32   13.260%   $258.5952   $258.60   $258.60   $258.60  
  Purchase #4 $53.77   5.414%   $56.6811   $56.68   $56.70   $56.70  
  Purchase #5 $136.55   4.603%   $142.8354   $142.84   $142.85   $142.80  
  Purchase #6 $116.58   5.204%   $122.6468   $122.65   $122.65   $122.60  
  Purchase #7 $157.36   3.792%   $163.3271   $163.33   $163.35   $163.30  
  7 purchase totals = $979.48       $1,064.6895   $1,064.71   $1,064.80   $1,064.60