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 $246.75   7.254%   $264.6492   $264.65   $264.65   $264.60  
  Purchase #2 $120.44   13.285%   $136.4405   $136.44   $136.45   $136.40  
  Purchase #3 $176.86   6.426%   $188.225   $188.23   $188.25   $188.20  
  Purchase #4 $148.64   12.812%   $167.6838   $167.68   $167.70   $167.70  
  Purchase #5 $125.91   7.306%   $135.109   $135.11   $135.10   $135.10  
  Purchase #6 $153.40   12.872%   $173.1456   $173.15   $173.15   $173.10  
  Purchase #7 $74.26   10.185%   $81.8234   $81.82   $81.80   $81.80  
  7 purchase totals = $1,046.26       $1,147.0765   $1,147.08   $1,147.10   $1,146.90