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 $216.90   4.481%   $226.6193   $226.62   $226.60   $226.60  
  Purchase #2 $228.61   11.478%   $254.8499   $254.85   $254.85   $254.80  
  Purchase #3 $115.86   11.121%   $128.7448   $128.74   $128.75   $128.70  
  Purchase #4 $11.82   3.452%   $12.228   $12.23   $12.25   $12.20  
  Purchase #5 $160.89   13.771%   $183.0462   $183.05   $183.05   $183.00  
  Purchase #6 $17.87   3.759%   $18.5417   $18.54   $18.55   $18.50  
  Purchase #7 $144.97   7.467%   $155.7949   $155.79   $155.80   $155.80  
  7 purchase totals = $896.92       $979.8248   $979.82   $979.85   $979.60