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 $154.47   13.642%   $175.5428   $175.54   $175.55   $175.50  
  Purchase #2 $59.46   9.312%   $64.9969   $65.00   $65.00   $65.00  
  Purchase #3 $243.65   9.790%   $267.5033   $267.50   $267.50   $267.50  
  Purchase #4 $139.80   11.871%   $156.3957   $156.40   $156.40   $156.40  
  Purchase #5 $98.53   4.192%   $102.6604   $102.66   $102.65   $102.70  
  Purchase #6 $237.76   6.835%   $254.0109   $254.01   $254.00   $254.00  
  Purchase #7 $169.61   5.464%   $178.8775   $178.88   $178.90   $178.90  
  7 purchase totals = $1,103.28       $1,199.9875   $1,199.99   $1,200.00   $1,200.00