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 $191.36   8.126%   $206.9099   $206.91   $206.90   $206.90  
  Purchase #2 $202.90   10.487%   $224.1781   $224.18   $224.20   $224.20  
  Purchase #3 $56.56   6.573%   $60.2777   $60.28   $60.30   $60.30  
  Purchase #4 $92.79   8.117%   $100.3218   $100.32   $100.30   $100.30  
  Purchase #5 $158.43   6.381%   $168.5394   $168.54   $168.55   $168.50  
  Purchase #6 $23.68   3.701%   $24.5564   $24.56   $24.55   $24.60  
  Purchase #7 $228.38   11.243%   $254.0568   $254.06   $254.05   $254.10  
  7 purchase totals = $954.10       $1,038.8401   $1,038.85   $1,038.85   $1,038.90