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 $168.59   13.700%   $191.6868   $191.69   $191.70   $191.70  
  Purchase #2 $73.82   10.782%   $81.7793   $81.78   $81.80   $81.80  
  Purchase #3 $56.67   6.437%   $60.3178   $60.32   $60.30   $60.30  
  Purchase #4 $184.30   6.157%   $195.6474   $195.65   $195.65   $195.60  
  Purchase #5 $108.99   11.531%   $121.5576   $121.56   $121.55   $121.60  
  Purchase #6 $241.74   3.577%   $250.387   $250.39   $250.40   $250.40  
  Purchase #7 $83.87   11.185%   $93.2509   $93.25   $93.25   $93.30  
  7 purchase totals = $917.98       $994.6268   $994.64   $994.65   $994.70