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 $206.95   11.654%   $231.068   $231.07   $231.05   $231.10  
  Purchase #2 $247.28   3.769%   $256.6   $256.60   $256.60   $256.60  
  Purchase #3 $169.67   10.147%   $186.8864   $186.89   $186.90   $186.90  
  Purchase #4 $167.70   3.317%   $173.2626   $173.26   $173.25   $173.30  
  Purchase #5 $101.89   7.633%   $109.6673   $109.67   $109.65   $109.70  
  Purchase #6 $227.85   10.265%   $251.2388   $251.24   $251.25   $251.20  
  Purchase #7 $146.93   6.114%   $155.9133   $155.91   $155.90   $155.90  
  7 purchase totals = $1,268.27       $1,364.6364   $1,364.64   $1,364.60   $1,364.70