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 $239.56   12.250%   $268.9061   $268.91   $268.90   $268.90  
  Purchase #2 $221.65   6.781%   $236.6801   $236.68   $236.70   $236.70  
  Purchase #3 $38.64   6.401%   $41.1133   $41.11   $41.10   $41.10  
  Purchase #4 $221.82   9.112%   $242.0322   $242.03   $242.05   $242.00  
  Purchase #5 $70.63   4.366%   $73.7137   $73.71   $73.70   $73.70  
  Purchase #6 $246.39   10.253%   $271.6524   $271.65   $271.65   $271.70  
  Purchase #7 $37.31   11.425%   $41.5727   $41.57   $41.55   $41.60  
  7 purchase totals = $1,076.00       $1,175.6705   $1,175.66   $1,175.65   $1,175.70