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 $226.63   8.557%   $246.0227   $246.02   $246.00   $246.00  
  Purchase #2 $58.76   11.189%   $65.3347   $65.33   $65.35   $65.30  
  Purchase #3 $133.27   12.827%   $150.3645   $150.36   $150.35   $150.40  
  Purchase #4 $181.48   3.132%   $187.164   $187.16   $187.15   $187.20  
  Purchase #5 $130.59   9.327%   $142.7701   $142.77   $142.75   $142.80  
  Purchase #6 $214.44   7.771%   $231.1041   $231.10   $231.10   $231.10  
  Purchase #7 $155.95   9.493%   $170.7543   $170.75   $170.75   $170.80  
  7 purchase totals = $1,101.12       $1,193.5144   $1,193.49   $1,193.45   $1,193.60