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 $187.60   9.253%   $204.9586   $204.96   $204.95   $205.00  
  Purchase #2 $202.77   10.643%   $224.3508   $224.35   $224.35   $224.40  
  Purchase #3 $239.69   13.211%   $271.3554   $271.36   $271.35   $271.40  
  Purchase #4 $119.52   5.602%   $126.2155   $126.22   $126.20   $126.20  
  Purchase #5 $86.31   6.841%   $92.2145   $92.21   $92.20   $92.20  
  Purchase #6 $250.74   7.287%   $269.0114   $269.01   $269.00   $269.00  
  Purchase #7 $55.62   5.262%   $58.5467   $58.55   $58.55   $58.50  
  7 purchase totals = $1,142.25       $1,246.6529   $1,246.66   $1,246.60   $1,246.70