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 $93.90   5.315%   $98.8908   $98.89   $98.90   $98.90  
  Purchase #2 $153.49   6.758%   $163.8629   $163.86   $163.85   $163.90  
  Purchase #3 $41.85   5.580%   $44.1852   $44.19   $44.20   $44.20  
  Purchase #4 $203.69   7.311%   $218.5818   $218.58   $218.60   $218.60  
  Purchase #5 $210.48   12.748%   $237.312   $237.31   $237.30   $237.30  
  Purchase #6 $86.99   5.261%   $91.5665   $91.57   $91.55   $91.60  
  Purchase #7 $141.38   4.325%   $147.4947   $147.49   $147.50   $147.50  
  7 purchase totals = $931.78       $1,001.8939   $1,001.89   $1,001.90   $1,002.00