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 $23.96   12.666%   $26.9948   $26.99   $27.00   $27.00  
  Purchase #2 $214.29   11.697%   $239.3555   $239.36   $239.35   $239.40  
  Purchase #3 $171.92   3.148%   $177.332   $177.33   $177.35   $177.30  
  Purchase #4 $50.94   7.538%   $54.7799   $54.78   $54.80   $54.80  
  Purchase #5 $167.46   4.464%   $174.9354   $174.94   $174.95   $174.90  
  Purchase #6 $90.32   3.614%   $93.5842   $93.58   $93.60   $93.60  
  Purchase #7 $228.76   5.603%   $241.5774   $241.58   $241.60   $241.60  
  7 purchase totals = $947.65       $1,008.5592   $1,008.56   $1,008.65   $1,008.60