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 $189.76   11.192%   $210.9979   $211.00   $211.00   $211.00  
  Purchase #2 $33.40   9.835%   $36.6849   $36.68   $36.70   $36.70  
  Purchase #3 $69.69   4.421%   $72.771   $72.77   $72.75   $72.80  
  Purchase #4 $84.65   8.755%   $92.0611   $92.06   $92.05   $92.10  
  Purchase #5 $198.76   13.827%   $226.2425   $226.24   $226.25   $226.20  
  Purchase #6 $144.84   13.231%   $164.0038   $164.00   $164.00   $164.00  
  Purchase #7 $122.25   5.608%   $129.1058   $129.11   $129.10   $129.10  
  7 purchase totals = $843.35       $931.8670   $931.86   $931.85   $931.90