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 $161.95   5.841%   $171.4095   $171.41   $171.40   $171.40  
  Purchase #2 $157.57   13.763%   $179.2564   $179.26   $179.25   $179.30  
  Purchase #3 $149.72   13.659%   $170.1703   $170.17   $170.15   $170.20  
  Purchase #4 $6.35   3.339%   $6.562   $6.56   $6.55   $6.60  
  Purchase #5 $56.40   12.760%   $63.5966   $63.60   $63.60   $63.60  
  Purchase #6 $237.58   13.628%   $269.9574   $269.96   $269.95   $270.00  
  Purchase #7 $146.40   11.677%   $163.4951   $163.50   $163.50   $163.50  
  7 purchase totals = $915.97       $1,024.4473   $1,024.46   $1,024.40   $1,024.60