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 $224.83   9.123%   $245.3412   $245.34   $245.35   $245.30  
  Purchase #2 $54.93   6.673%   $58.5955   $58.60   $58.60   $58.60  
  Purchase #3 $38.38   5.723%   $40.5765   $40.58   $40.60   $40.60  
  Purchase #4 $157.45   10.724%   $174.3349   $174.33   $174.35   $174.30  
  Purchase #5 $185.86   13.803%   $211.5143   $211.51   $211.50   $211.50  
  Purchase #6 $194.55   6.846%   $207.8689   $207.87   $207.85   $207.90  
  Purchase #7 $112.36   12.408%   $126.3016   $126.30   $126.30   $126.30  
  7 purchase totals = $968.36       $1,064.5329   $1,064.53   $1,064.55   $1,064.50