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 $181.63   12.782%   $204.8459   $204.85   $204.85   $204.80  
  Purchase #2 $43.28   7.270%   $46.4265   $46.43   $46.45   $46.40  
  Purchase #3 $95.32   10.468%   $105.2981   $105.30   $105.30   $105.30  
  Purchase #4 $218.86   7.143%   $234.4932   $234.49   $234.50   $234.50  
  Purchase #5 $161.42   12.629%   $181.8057   $181.81   $181.80   $181.80  
  Purchase #6 $99.42   7.419%   $106.796   $106.80   $106.80   $106.80  
  Purchase #7 $177.53   5.125%   $186.6284   $186.63   $186.65   $186.60  
  7 purchase totals = $977.46       $1,066.2938   $1,066.31   $1,066.35   $1,066.20