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 $167.58   5.768%   $177.246   $177.25   $177.25   $177.20  
  Purchase #2 $87.57   6.657%   $93.3995   $93.40   $93.40   $93.40  
  Purchase #3 $112.95   13.391%   $128.0751   $128.08   $128.10   $128.10  
  Purchase #4 $141.63   13.740%   $161.09   $161.09   $161.10   $161.10  
  Purchase #5 $162.64   12.349%   $182.7244   $182.72   $182.70   $182.70  
  Purchase #6 $94.66   7.388%   $101.6535   $101.65   $101.65   $101.70  
  Purchase #7 $141.29   5.789%   $149.4693   $149.47   $149.45   $149.50  
  7 purchase totals = $908.32       $993.6578   $993.66   $993.65   $993.70