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 $77.85   10.480%   $86.0087   $86.01   $86.00   $86.00  
  Purchase #2 $215.93   11.115%   $239.9306   $239.93   $239.95   $239.90  
  Purchase #3 $109.45   11.424%   $121.9536   $121.95   $121.95   $122.00  
  Purchase #4 $102.90   13.204%   $116.4869   $116.49   $116.50   $116.50  
  Purchase #5 $161.90   6.354%   $172.1871   $172.19   $172.20   $172.20  
  Purchase #6 $200.45   10.193%   $220.8819   $220.88   $220.90   $220.90  
  Purchase #7 $91.50   7.754%   $98.5949   $98.59   $98.60   $98.60  
  7 purchase totals = $959.98       $1,056.0437   $1,056.04   $1,056.10   $1,056.10