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 $137.30   5.343%   $144.6359   $144.64   $144.65   $144.60  
  Purchase #2 $9.45   6.421%   $10.0568   $10.06   $10.05   $10.10  
  Purchase #3 $249.48   7.422%   $267.9964   $268.00   $268.00   $268.00  
  Purchase #4 $34.81   11.143%   $38.6889   $38.69   $38.70   $38.70  
  Purchase #5 $215.60   12.280%   $242.0757   $242.08   $242.10   $242.10  
  Purchase #6 $221.94   8.469%   $240.7361   $240.74   $240.75   $240.70  
  Purchase #7 $240.52   6.221%   $255.4827   $255.48   $255.50   $255.50  
  7 purchase totals = $1,109.10       $1,199.6725   $1,199.69   $1,199.75   $1,199.70