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 $184.49   9.517%   $202.0479   $202.05   $202.05   $202.00  
  Purchase #2 $148.97   5.174%   $156.6777   $156.68   $156.70   $156.70  
  Purchase #3 $184.43   9.622%   $202.1759   $202.18   $202.20   $202.20  
  Purchase #4 $26.52   12.541%   $29.8459   $29.85   $29.85   $29.80  
  Purchase #5 $250.26   6.349%   $266.149   $266.15   $266.15   $266.10  
  Purchase #6 $98.37   13.693%   $111.8398   $111.84   $111.85   $111.80  
  Purchase #7 $95.70   8.574%   $103.9053   $103.91   $103.90   $103.90  
  7 purchase totals = $988.74       $1,072.6415   $1,072.66   $1,072.70   $1,072.50