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 $125.51   4.558%   $131.2307   $131.23   $131.25   $131.20  
  Purchase #2 $189.74   10.795%   $210.2224   $210.22   $210.20   $210.20  
  Purchase #3 $55.44   11.835%   $62.0013   $62.00   $62.00   $62.00  
  Purchase #4 $128.57   13.395%   $145.792   $145.79   $145.80   $145.80  
  Purchase #5 $215.87   4.512%   $225.6101   $225.61   $225.60   $225.60  
  Purchase #6 $233.27   9.387%   $255.1671   $255.17   $255.15   $255.20  
  Purchase #7 $125.88   10.570%   $139.1855   $139.19   $139.20   $139.20  
  7 purchase totals = $1,074.28       $1,169.2091   $1,169.21   $1,169.20   $1,169.20