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 $102.47   13.873%   $116.6857   $116.69   $116.70   $116.70  
  Purchase #2 $5.25   13.728%   $5.9707   $5.97   $5.95   $6.00  
  Purchase #3 $237.39   9.860%   $260.7967   $260.80   $260.80   $260.80  
  Purchase #4 $216.39   12.667%   $243.8001   $243.80   $243.80   $243.80  
  Purchase #5 $90.62   8.112%   $97.9711   $97.97   $97.95   $98.00  
  Purchase #6 $52.61   3.154%   $54.2693   $54.27   $54.25   $54.30  
  Purchase #7 $223.73   10.231%   $246.6198   $246.62   $246.60   $246.60  
  7 purchase totals = $928.46       $1,026.1134   $1,026.12   $1,026.05   $1,026.20