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 $157.95   5.104%   $166.0118   $166.01   $166.00   $166.00  
  Purchase #2 $8.65   6.307%   $9.1956   $9.20   $9.20   $9.20  
  Purchase #3 $70.74   6.423%   $75.2836   $75.28   $75.30   $75.30  
  Purchase #4 $239.77   13.866%   $273.0165   $273.02   $273.00   $273.00  
  Purchase #5 $105.97   6.841%   $113.2194   $113.22   $113.20   $113.20  
  Purchase #6 $137.53   9.249%   $150.2501   $150.25   $150.25   $150.30  
  Purchase #7 $152.56   4.241%   $159.0301   $159.03   $159.05   $159.00  
  7 purchase totals = $873.17       $946.0071   $946.01   $946.00   $946.00