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 $186.41   10.484%   $205.9532   $205.95   $205.95   $206.00  
  Purchase #2 $131.52   10.155%   $144.8759   $144.88   $144.90   $144.90  
  Purchase #3 $24.39   12.265%   $27.3814   $27.38   $27.40   $27.40  
  Purchase #4 $129.33   3.790%   $134.2316   $134.23   $134.25   $134.20  
  Purchase #5 $9.42   7.725%   $10.1477   $10.15   $10.15   $10.10  
  Purchase #6 $181.55   12.479%   $204.2056   $204.21   $204.20   $204.20  
  Purchase #7 $242.37   6.785%   $258.8148   $258.81   $258.80   $258.80  
  7 purchase totals = $904.99       $985.6102   $985.61   $985.65   $985.60