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 $250.81   7.569%   $269.7938   $269.79   $269.80   $269.80  
  Purchase #2 $191.75   8.247%   $207.5636   $207.56   $207.55   $207.60  
  Purchase #3 $117.31   5.852%   $124.175   $124.18   $124.20   $124.20  
  Purchase #4 $26.80   6.380%   $28.5098   $28.51   $28.50   $28.50  
  Purchase #5 $237.34   11.234%   $264.0028   $264.00   $264.00   $264.00  
  Purchase #6 $228.34   5.728%   $241.4193   $241.42   $241.40   $241.40  
  Purchase #7 $84.65   13.111%   $95.7485   $95.75   $95.75   $95.70  
  7 purchase totals = $1,137.00       $1,231.2128   $1,231.21   $1,231.20   $1,231.20