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 $72.52   4.872%   $76.0532   $76.05   $76.05   $76.10  
  Purchase #2 $128.60   11.705%   $143.6526   $143.65   $143.65   $143.70  
  Purchase #3 $193.91   7.138%   $207.7513   $207.75   $207.75   $207.80  
  Purchase #4 $32.58   4.135%   $33.9272   $33.93   $33.95   $33.90  
  Purchase #5 $66.29   13.465%   $75.2159   $75.22   $75.20   $75.20  
  Purchase #6 $210.39   4.428%   $219.7061   $219.71   $219.70   $219.70  
  Purchase #7 $143.52   7.346%   $154.063   $154.06   $154.05   $154.10  
  7 purchase totals = $847.81       $910.3693   $910.37   $910.35   $910.50