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 $148.43   11.810%   $165.9596   $165.96   $165.95   $166.00  
  Purchase #2 $152.96   3.204%   $157.8608   $157.86   $157.85   $157.90  
  Purchase #3 $161.99   12.121%   $181.6248   $181.62   $181.60   $181.60  
  Purchase #4 $206.51   12.700%   $232.7368   $232.74   $232.75   $232.70  
  Purchase #5 $197.40   4.843%   $206.9601   $206.96   $206.95   $207.00  
  Purchase #6 $77.51   5.681%   $81.9133   $81.91   $81.90   $81.90  
  Purchase #7 $54.88   6.767%   $58.5937   $58.59   $58.60   $58.60  
  7 purchase totals = $999.68       $1,085.6491   $1,085.64   $1,085.60   $1,085.70