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 $7.96   6.794%   $8.5008   $8.50   $8.50   $8.50  
  Purchase #2 $87.79   8.456%   $95.2135   $95.21   $95.20   $95.20  
  Purchase #3 $191.72   7.444%   $205.9916   $205.99   $206.00   $206.00  
  Purchase #4 $213.39   12.397%   $239.844   $239.84   $239.85   $239.80  
  Purchase #5 $220.87   7.149%   $236.66   $236.66   $236.65   $236.70  
  Purchase #6 $190.48   12.644%   $214.5643   $214.56   $214.55   $214.60  
  Purchase #7 $193.56   4.254%   $201.794   $201.79   $201.80   $201.80  
  7 purchase totals = $1,105.77       $1,202.5682   $1,202.55   $1,202.55   $1,202.60