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 $244.51   3.172%   $252.2659   $252.27   $252.25   $252.30  
  Purchase #2 $146.29   13.784%   $166.4546   $166.45   $166.45   $166.50  
  Purchase #3 $47.44   12.444%   $53.3434   $53.34   $53.35   $53.30  
  Purchase #4 $23.73   3.515%   $24.5641   $24.56   $24.55   $24.60  
  Purchase #5 $178.70   4.229%   $186.2572   $186.26   $186.25   $186.30  
  Purchase #6 $250.39   4.776%   $262.3486   $262.35   $262.35   $262.30  
  Purchase #7 $204.55   10.690%   $226.4164   $226.42   $226.40   $226.40  
  7 purchase totals = $1,095.61       $1,171.6502   $1,171.65   $1,171.60   $1,171.70