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 $168.86   9.372%   $184.6856   $184.69   $184.70   $184.70  
  Purchase #2 $165.69   3.548%   $171.5687   $171.57   $171.55   $171.60  
  Purchase #3 $173.36   7.500%   $186.362   $186.36   $186.35   $186.40  
  Purchase #4 $244.29   12.469%   $274.7505   $274.75   $274.75   $274.80  
  Purchase #5 $156.61   7.500%   $168.3558   $168.36   $168.35   $168.40  
  Purchase #6 $156.55   9.541%   $171.4864   $171.49   $171.50   $171.50  
  Purchase #7 $181.72   11.807%   $203.1757   $203.18   $203.20   $203.20  
  7 purchase totals = $1,247.08       $1,360.3847   $1,360.40   $1,360.40   $1,360.60