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 $231.68   9.163%   $252.9088   $252.91   $252.90   $252.90  
  Purchase #2 $116.90   11.314%   $130.1261   $130.13   $130.15   $130.10  
  Purchase #3 $107.53   9.309%   $117.54   $117.54   $117.55   $117.50  
  Purchase #4 $128.90   4.449%   $134.6348   $134.63   $134.65   $134.60  
  Purchase #5 $67.36   7.842%   $72.6424   $72.64   $72.65   $72.60  
  Purchase #6 $118.35   13.522%   $134.3533   $134.35   $134.35   $134.40  
  Purchase #7 $170.36   7.774%   $183.6038   $183.60   $183.60   $183.60  
  7 purchase totals = $941.08       $1,025.8092   $1,025.80   $1,025.85   $1,025.70