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 $232.80   12.771%   $262.5309   $262.53   $262.55   $262.50  
  Purchase #2 $105.74   4.219%   $110.2012   $110.20   $110.20   $110.20  
  Purchase #3 $96.82   13.165%   $109.5664   $109.57   $109.55   $109.60  
  Purchase #4 $161.58   10.786%   $179.008   $179.01   $179.00   $179.00  
  Purchase #5 $5.97   6.732%   $6.3719   $6.37   $6.35   $6.40  
  Purchase #6 $153.88   13.604%   $174.8138   $174.81   $174.80   $174.80  
  Purchase #7 $250.27   6.850%   $267.4135   $267.41   $267.40   $267.40  
  7 purchase totals = $1,007.06       $1,109.9057   $1,109.90   $1,109.85   $1,109.90