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 $165.54   12.724%   $186.6033   $186.60   $186.60   $186.60  
  Purchase #2 $8.44   6.613%   $8.9981   $9.00   $9.00   $9.00  
  Purchase #3 $96.71   7.756%   $104.2108   $104.21   $104.20   $104.20  
  Purchase #4 $208.45   13.446%   $236.4782   $236.48   $236.50   $236.50  
  Purchase #5 $34.78   6.439%   $37.0195   $37.02   $37.00   $37.00  
  Purchase #6 $202.70   8.481%   $219.891   $219.89   $219.90   $219.90  
  Purchase #7 $22.52   6.238%   $23.9248   $23.92   $23.90   $23.90  
  7 purchase totals = $739.14       $817.1257   $817.12   $817.10   $817.10