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 $95.84   3.183%   $98.8906   $98.89   $98.90   $98.90  
  Purchase #2 $62.58   4.700%   $65.5213   $65.52   $65.50   $65.50  
  Purchase #3 $98.33   12.555%   $110.6753   $110.68   $110.70   $110.70  
  Purchase #4 $165.70   12.856%   $187.0024   $187.00   $187.00   $187.00  
  Purchase #5 $198.64   4.862%   $208.2979   $208.30   $208.30   $208.30  
  Purchase #6 $92.38   8.486%   $100.2194   $100.22   $100.20   $100.20  
  Purchase #7 $87.65   12.382%   $98.5028   $98.50   $98.50   $98.50  
  7 purchase totals = $801.12       $869.1097   $869.11   $869.10   $869.10