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 $24.40   10.859%   $27.0496   $27.05   $27.05   $27.00  
  Purchase #2 $178.96   13.601%   $203.3003   $203.30   $203.30   $203.30  
  Purchase #3 $121.64   10.401%   $134.2918   $134.29   $134.30   $134.30  
  Purchase #4 $97.49   10.409%   $107.6377   $107.64   $107.65   $107.60  
  Purchase #5 $228.51   12.802%   $257.7639   $257.76   $257.75   $257.80  
  Purchase #6 $73.47   6.120%   $77.9664   $77.97   $77.95   $78.00  
  Purchase #7 $244.75   4.208%   $255.0491   $255.05   $255.05   $255.00  
  7 purchase totals = $969.22       $1,063.0588   $1,063.06   $1,063.05   $1,063.00