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 $39.95   11.690%   $44.6202   $44.62   $44.60   $44.60  
  Purchase #2 $231.64   10.415%   $255.7653   $255.77   $255.75   $255.80  
  Purchase #3 $26.65   4.316%   $27.8002   $27.80   $27.80   $27.80  
  Purchase #4 $222.43   9.577%   $243.7321   $243.73   $243.75   $243.70  
  Purchase #5 $92.77   11.601%   $103.5322   $103.53   $103.55   $103.50  
  Purchase #6 $249.74   12.755%   $281.5943   $281.59   $281.60   $281.60  
  Purchase #7 $212.44   7.642%   $228.6747   $228.67   $228.65   $228.70  
  7 purchase totals = $1,075.62       $1,185.7190   $1,185.71   $1,185.70   $1,185.70