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 $167.94   11.830%   $187.8073   $187.81   $187.80   $187.80  
  Purchase #2 $49.73   11.198%   $55.2988   $55.30   $55.30   $55.30  
  Purchase #3 $124.89   7.620%   $134.4066   $134.41   $134.40   $134.40  
  Purchase #4 $181.42   11.656%   $202.5663   $202.57   $202.55   $202.60  
  Purchase #5 $232.44   4.341%   $242.5302   $242.53   $242.55   $242.50  
  Purchase #6 $114.72   3.567%   $118.8121   $118.81   $118.80   $118.80  
  Purchase #7 $59.70   9.262%   $65.2294   $65.23   $65.25   $65.20  
  7 purchase totals = $930.84       $1,006.6507   $1,006.66   $1,006.65   $1,006.60