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 $126.75   7.546%   $136.3146   $136.31   $136.30   $136.30  
  Purchase #2 $182.38   7.621%   $196.2792   $196.28   $196.30   $196.30  
  Purchase #3 $8.52   8.403%   $9.2359   $9.24   $9.25   $9.20  
  Purchase #4 $235.97   6.790%   $251.9924   $251.99   $252.00   $252.00  
  Purchase #5 $192.77   8.393%   $208.9492   $208.95   $208.95   $208.90  
  Purchase #6 $56.51   10.718%   $62.5667   $62.57   $62.55   $62.60  
  Purchase #7 $138.90   8.360%   $150.512   $150.51   $150.50   $150.50  
  7 purchase totals = $941.80       $1,015.8500   $1,015.85   $1,015.85   $1,015.80