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 $168.70   13.359%   $191.2366   $191.24   $191.25   $191.20  
  Purchase #2 $218.76   8.307%   $236.9324   $236.93   $236.95   $236.90  
  Purchase #3 $229.87   9.416%   $251.5146   $251.51   $251.50   $251.50  
  Purchase #4 $215.45   6.600%   $229.6697   $229.67   $229.65   $229.70  
  Purchase #5 $117.81   3.549%   $121.9911   $121.99   $122.00   $122.00  
  Purchase #6 $43.79   9.198%   $47.8178   $47.82   $47.80   $47.80  
  Purchase #7 $165.39   5.704%   $174.8238   $174.82   $174.80   $174.80  
  7 purchase totals = $1,159.77       $1,253.9860   $1,253.98   $1,253.95   $1,253.90