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 $246.39   8.731%   $267.9023   $267.90   $267.90   $267.90  
  Purchase #2 $60.55   5.169%   $63.6798   $63.68   $63.70   $63.70  
  Purchase #3 $155.63   12.783%   $175.5242   $175.52   $175.50   $175.50  
  Purchase #4 $191.34   11.557%   $213.4532   $213.45   $213.45   $213.50  
  Purchase #5 $126.77   7.768%   $136.6175   $136.62   $136.60   $136.60  
  Purchase #6 $68.56   5.157%   $72.0956   $72.10   $72.10   $72.10  
  Purchase #7 $23.48   7.651%   $25.2765   $25.28   $25.30   $25.30  
  7 purchase totals = $872.72       $954.5491   $954.55   $954.55   $954.60