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 $187.57   8.269%   $203.0802   $203.08   $203.10   $203.10  
  Purchase #2 $62.86   3.463%   $65.0368   $65.04   $65.05   $65.00  
  Purchase #3 $66.85   6.261%   $71.0355   $71.04   $71.05   $71.00  
  Purchase #4 $94.61   13.359%   $107.2489   $107.25   $107.25   $107.20  
  Purchase #5 $240.33   11.513%   $267.9992   $268.00   $268.00   $268.00  
  Purchase #6 $78.96   8.378%   $85.5753   $85.58   $85.60   $85.60  
  Purchase #7 $209.87   5.423%   $221.2513   $221.25   $221.25   $221.30  
  7 purchase totals = $941.05       $1,021.2272   $1,021.24   $1,021.30   $1,021.20