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 $199.74   11.549%   $222.808   $222.81   $222.80   $222.80  
  Purchase #2 $85.51   9.175%   $93.3555   $93.36   $93.35   $93.40  
  Purchase #3 $241.56   7.487%   $259.6456   $259.65   $259.65   $259.60  
  Purchase #4 $132.37   4.160%   $137.8766   $137.88   $137.90   $137.90  
  Purchase #5 $53.30   6.784%   $56.9159   $56.92   $56.90   $56.90  
  Purchase #6 $24.86   5.729%   $26.2842   $26.28   $26.30   $26.30  
  Purchase #7 $218.64   8.245%   $236.6669   $236.67   $236.65   $236.70  
  7 purchase totals = $955.98       $1,033.5527   $1,033.57   $1,033.55   $1,033.60