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 $248.66   4.628%   $260.168   $260.17   $260.15   $260.20  
  Purchase #2 $211.78   3.838%   $219.9081   $219.91   $219.90   $219.90  
  Purchase #3 $165.68   8.427%   $179.6419   $179.64   $179.65   $179.60  
  Purchase #4 $44.32   7.545%   $47.6639   $47.66   $47.65   $47.70  
  Purchase #5 $62.39   5.162%   $65.6106   $65.61   $65.60   $65.60  
  Purchase #6 $52.41   5.543%   $55.3151   $55.32   $55.30   $55.30  
  Purchase #7 $72.42   4.841%   $75.9259   $75.93   $75.95   $75.90  
  7 purchase totals = $857.66       $904.2335   $904.24   $904.20   $904.20