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 $54.87   3.232%   $56.6434   $56.64   $56.65   $56.60  
  Purchase #2 $212.76   11.437%   $237.0934   $237.09   $237.10   $237.10  
  Purchase #3 $176.66   6.478%   $188.104   $188.10   $188.10   $188.10  
  Purchase #4 $61.33   10.108%   $67.5292   $67.53   $67.55   $67.50  
  Purchase #5 $150.93   10.580%   $166.8984   $166.90   $166.90   $166.90  
  Purchase #6 $240.42   5.817%   $254.4052   $254.41   $254.40   $254.40  
  Purchase #7 $107.49   5.173%   $113.0505   $113.05   $113.05   $113.10  
  7 purchase totals = $1,004.46       $1,083.7241   $1,083.72   $1,083.75   $1,083.70