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 $236.36   11.576%   $263.721   $263.72   $263.70   $263.70  
  Purchase #2 $12.45   13.114%   $14.0827   $14.08   $14.10   $14.10  
  Purchase #3 $105.99   11.580%   $118.2636   $118.26   $118.25   $118.30  
  Purchase #4 $67.62   6.215%   $71.8226   $71.82   $71.80   $71.80  
  Purchase #5 $77.32   8.781%   $84.1095   $84.11   $84.10   $84.10  
  Purchase #6 $162.79   7.253%   $174.5972   $174.60   $174.60   $174.60  
  Purchase #7 $14.25   5.278%   $15.0021   $15.00   $15.00   $15.00  
  7 purchase totals = $676.78       $741.5987   $741.59   $741.55   $741.60