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 $93.80   5.706%   $99.1522   $99.15   $99.15   $99.20  
  Purchase #2 $248.46   5.484%   $262.0855   $262.09   $262.10   $262.10  
  Purchase #3 $159.85   5.449%   $168.5602   $168.56   $168.55   $168.60  
  Purchase #4 $25.94   5.854%   $27.4585   $27.46   $27.45   $27.50  
  Purchase #5 $120.63   11.567%   $134.5833   $134.58   $134.60   $134.60  
  Purchase #6 $210.40   12.521%   $236.7442   $236.74   $236.75   $236.70  
  Purchase #7 $130.67   13.242%   $147.9733   $147.97   $147.95   $148.00  
  7 purchase totals = $989.75       $1,076.5572   $1,076.55   $1,076.55   $1,076.70