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 $134.69   12.273%   $151.2205   $151.22   $151.20   $151.20  
  Purchase #2 $175.55   3.678%   $182.0067   $182.01   $182.00   $182.00  
  Purchase #3 $200.53   9.462%   $219.5041   $219.50   $219.50   $219.50  
  Purchase #4 $58.42   5.654%   $61.7231   $61.72   $61.70   $61.70  
  Purchase #5 $187.43   4.561%   $195.9787   $195.98   $196.00   $196.00  
  Purchase #6 $125.66   5.835%   $132.9923   $132.99   $133.00   $133.00  
  Purchase #7 $241.83   10.327%   $266.8038   $266.80   $266.80   $266.80  
  7 purchase totals = $1,124.11       $1,210.2292   $1,210.22   $1,210.20   $1,210.20