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 $186.60   6.779%   $199.2496   $199.25   $199.25   $199.20  
  Purchase #2 $241.89   10.375%   $266.9861   $266.99   $267.00   $267.00  
  Purchase #3 $111.56   6.292%   $118.5794   $118.58   $118.60   $118.60  
  Purchase #4 $204.44   12.334%   $229.6556   $229.66   $229.65   $229.70  
  Purchase #5 $199.51   5.321%   $210.1259   $210.13   $210.15   $210.10  
  Purchase #6 $181.67   9.665%   $199.2284   $199.23   $199.25   $199.20  
  Purchase #7 $81.61   10.586%   $90.2492   $90.25   $90.25   $90.20  
  7 purchase totals = $1,207.28       $1,314.0742   $1,314.09   $1,314.15   $1,314.00