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 $217.82   8.628%   $236.6135   $236.61   $236.60   $236.60  
  Purchase #2 $26.52   5.768%   $28.0497   $28.05   $28.05   $28.00  
  Purchase #3 $54.70   12.718%   $61.6567   $61.66   $61.65   $61.70  
  Purchase #4 $53.52   11.701%   $59.7824   $59.78   $59.80   $59.80  
  Purchase #5 $15.51   10.501%   $17.1387   $17.14   $17.15   $17.10  
  Purchase #6 $191.57   3.354%   $197.9953   $198.00   $198.00   $198.00  
  Purchase #7 $176.44   10.140%   $194.331   $194.33   $194.35   $194.30  
  7 purchase totals = $736.08       $795.5673   $795.57   $795.60   $795.50