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 $239.55   5.308%   $252.2653   $252.27   $252.25   $252.30  
  Purchase #2 $215.44   13.814%   $245.2009   $245.20   $245.20   $245.20  
  Purchase #3 $110.37   9.508%   $120.864   $120.86   $120.85   $120.90  
  Purchase #4 $177.45   12.528%   $199.6809   $199.68   $199.70   $199.70  
  Purchase #5 $22.36   9.642%   $24.516   $24.52   $24.50   $24.50  
  Purchase #6 $146.68   8.805%   $159.5952   $159.60   $159.60   $159.60  
  Purchase #7 $206.90   11.226%   $230.1266   $230.13   $230.15   $230.10  
  7 purchase totals = $1,118.75       $1,232.2489   $1,232.26   $1,232.25   $1,232.30