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 $215.51   7.508%   $231.6905   $231.69   $231.70   $231.70  
  Purchase #2 $125.58   10.336%   $138.5599   $138.56   $138.55   $138.60  
  Purchase #3 $73.36   10.557%   $81.1046   $81.10   $81.10   $81.10  
  Purchase #4 $114.60   13.306%   $129.8487   $129.85   $129.85   $129.80  
  Purchase #5 $11.60   12.374%   $13.0354   $13.04   $13.05   $13.00  
  Purchase #6 $205.56   3.860%   $213.4946   $213.49   $213.50   $213.50  
  Purchase #7 $170.67   13.557%   $193.8077   $193.81   $193.80   $193.80  
  7 purchase totals = $916.88       $1,001.5414   $1,001.54   $1,001.55   $1,001.50