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 $88.62   10.543%   $97.9632   $97.96   $97.95   $98.00  
  Purchase #2 $62.28   5.214%   $65.5273   $65.53   $65.55   $65.50  
  Purchase #3 $92.27   6.811%   $98.5545   $98.55   $98.55   $98.60  
  Purchase #4 $98.82   12.406%   $111.0796   $111.08   $111.10   $111.10  
  Purchase #5 $85.39   11.281%   $95.0228   $95.02   $95.00   $95.00  
  Purchase #6 $223.51   3.838%   $232.0883   $232.09   $232.10   $232.10  
  Purchase #7 $91.54   5.849%   $96.8942   $96.89   $96.90   $96.90  
  7 purchase totals = $742.43       $797.1299   $797.12   $797.15   $797.20