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 $29.67   10.237%   $32.7073   $32.71   $32.70   $32.70  
  Purchase #2 $249.82   6.420%   $265.8584   $265.86   $265.85   $265.90  
  Purchase #3 $51.38   10.467%   $56.7579   $56.76   $56.75   $56.80  
  Purchase #4 $160.77   12.537%   $180.9257   $180.93   $180.95   $180.90  
  Purchase #5 $190.85   12.224%   $214.1795   $214.18   $214.20   $214.20  
  Purchase #6 $142.62   6.705%   $152.1827   $152.18   $152.20   $152.20  
  Purchase #7 $220.51   10.467%   $243.5908   $243.59   $243.60   $243.60  
  7 purchase totals = $1,045.62       $1,146.2023   $1,146.21   $1,146.25   $1,146.30