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 $125.46   12.159%   $140.7147   $140.71   $140.70   $140.70  
  Purchase #2 $114.83   10.126%   $126.4577   $126.46   $126.45   $126.50  
  Purchase #3 $63.39   5.199%   $66.6856   $66.69   $66.70   $66.70  
  Purchase #4 $165.62   5.625%   $174.9361   $174.94   $174.95   $174.90  
  Purchase #5 $217.62   13.790%   $247.6298   $247.63   $247.65   $247.60  
  Purchase #6 $211.55   5.823%   $223.8686   $223.87   $223.85   $223.90  
  Purchase #7 $56.48   3.670%   $58.5528   $58.55   $58.55   $58.60  
  7 purchase totals = $954.95       $1,038.8453   $1,038.85   $1,038.85   $1,038.90