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 $146.84   10.781%   $162.6708   $162.67   $162.65   $162.70  
  Purchase #2 $211.34   7.290%   $226.7467   $226.75   $226.75   $226.70  
  Purchase #3 $45.57   7.189%   $48.846   $48.85   $48.85   $48.80  
  Purchase #4 $222.82   10.627%   $246.4991   $246.50   $246.50   $246.50  
  Purchase #5 $170.89   3.156%   $176.2833   $176.28   $176.30   $176.30  
  Purchase #6 $72.55   10.224%   $79.9675   $79.97   $79.95   $80.00  
  Purchase #7 $122.62   3.428%   $126.8234   $126.82   $126.80   $126.80  
  7 purchase totals = $992.63       $1,067.8368   $1,067.84   $1,067.80   $1,067.80