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 $69.33   4.563%   $72.4935   $72.49   $72.50   $72.50  
  Purchase #2 $243.97   11.166%   $271.2117   $271.21   $271.20   $271.20  
  Purchase #3 $86.37   10.380%   $95.3352   $95.34   $95.35   $95.30  
  Purchase #4 $119.77   8.181%   $129.5684   $129.57   $129.55   $129.60  
  Purchase #5 $188.39   9.783%   $206.8202   $206.82   $206.80   $206.80  
  Purchase #6 $75.62   9.294%   $82.6481   $82.65   $82.65   $82.60  
  Purchase #7 $145.39   5.805%   $153.8299   $153.83   $153.85   $153.80  
  7 purchase totals = $928.84       $1,011.9070   $1,011.91   $1,011.90   $1,011.80