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 $154.54   5.106%   $162.4308   $162.43   $162.45   $162.40  
  Purchase #2 $153.25   5.527%   $161.7201   $161.72   $161.70   $161.70  
  Purchase #3 $220.64   10.171%   $243.0813   $243.08   $243.10   $243.10  
  Purchase #4 $96.65   5.702%   $102.161   $102.16   $102.15   $102.20  
  Purchase #5 $161.74   7.113%   $173.2446   $173.24   $173.25   $173.20  
  Purchase #6 $166.90   4.418%   $174.2736   $174.27   $174.25   $174.30  
  Purchase #7 $45.64   11.532%   $50.9032   $50.90   $50.90   $50.90  
  7 purchase totals = $999.36       $1,067.8146   $1,067.80   $1,067.80   $1,067.80