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 $157.59   6.797%   $168.3014   $168.30   $168.30   $168.30  
  Purchase #2 $107.79   8.201%   $116.6299   $116.63   $116.65   $116.60  
  Purchase #3 $182.88   10.765%   $202.567   $202.57   $202.55   $202.60  
  Purchase #4 $172.26   8.161%   $186.3181   $186.32   $186.30   $186.30  
  Purchase #5 $231.38   8.330%   $250.654   $250.65   $250.65   $250.70  
  Purchase #6 $181.31   8.124%   $196.0396   $196.04   $196.05   $196.00  
  Purchase #7 $156.92   11.328%   $174.6959   $174.70   $174.70   $174.70  
  7 purchase totals = $1,190.13       $1,295.2059   $1,295.21   $1,295.20   $1,295.20