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 $196.37   3.241%   $202.7344   $202.73   $202.75   $202.70  
  Purchase #2 $188.96   4.524%   $197.5086   $197.51   $197.50   $197.50  
  Purchase #3 $127.30   6.763%   $135.9093   $135.91   $135.90   $135.90  
  Purchase #4 $99.25   4.670%   $103.885   $103.89   $103.90   $103.90  
  Purchase #5 $162.36   13.261%   $183.8906   $183.89   $183.90   $183.90  
  Purchase #6 $196.29   12.560%   $220.944   $220.94   $220.95   $220.90  
  Purchase #7 $89.64   3.255%   $92.5578   $92.56   $92.55   $92.60  
  7 purchase totals = $1,060.17       $1,137.4297   $1,137.43   $1,137.45   $1,137.40