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 $156.64   3.343%   $161.8765   $161.88   $161.90   $161.90  
  Purchase #2 $178.98   13.513%   $203.1656   $203.17   $203.15   $203.20  
  Purchase #3 $76.28   11.794%   $85.2765   $85.28   $85.30   $85.30  
  Purchase #4 $91.73   5.707%   $96.965   $96.97   $96.95   $97.00  
  Purchase #5 $55.86   7.541%   $60.0724   $60.07   $60.05   $60.10  
  Purchase #6 $238.75   7.683%   $257.0932   $257.09   $257.10   $257.10  
  Purchase #7 $228.52   11.632%   $255.1014   $255.10   $255.10   $255.10  
  7 purchase totals = $1,026.76       $1,119.5506   $1,119.56   $1,119.55   $1,119.70