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 $55.92   11.531%   $62.3681   $62.37   $62.35   $62.40  
  Purchase #2 $178.52   11.267%   $198.6338   $198.63   $198.65   $198.60  
  Purchase #3 $171.94   5.592%   $181.5549   $181.55   $181.55   $181.60  
  Purchase #4 $229.87   13.227%   $260.2749   $260.27   $260.25   $260.30  
  Purchase #5 $89.69   11.723%   $100.2044   $100.20   $100.20   $100.20  
  Purchase #6 $176.95   4.348%   $184.6438   $184.64   $184.65   $184.60  
  Purchase #7 $184.99   9.227%   $202.059   $202.06   $202.05   $202.10  
  7 purchase totals = $1,087.88       $1,189.7389   $1,189.72   $1,189.70   $1,189.80