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 $62.74   7.676%   $67.5559   $67.56   $67.55   $67.60  
  Purchase #2 $210.88   6.796%   $225.2114   $225.21   $225.20   $225.20  
  Purchase #3 $156.28   9.383%   $170.9438   $170.94   $170.95   $170.90  
  Purchase #4 $178.65   4.225%   $186.198   $186.20   $186.20   $186.20  
  Purchase #5 $202.83   7.557%   $218.1579   $218.16   $218.15   $218.20  
  Purchase #6 $219.65   5.415%   $231.544   $231.54   $231.55   $231.50  
  Purchase #7 $133.60   13.132%   $151.1444   $151.14   $151.15   $151.10  
  7 purchase totals = $1,164.63       $1,250.7554   $1,250.75   $1,250.75   $1,250.70