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 $67.76   12.704%   $76.3682   $76.37   $76.35   $76.40  
  Purchase #2 $175.74   5.661%   $185.6886   $185.69   $185.70   $185.70  
  Purchase #3 $219.65   4.838%   $230.2767   $230.28   $230.30   $230.30  
  Purchase #4 $236.25   9.551%   $258.8142   $258.81   $258.80   $258.80  
  Purchase #5 $98.56   9.683%   $108.1036   $108.10   $108.10   $108.10  
  Purchase #6 $16.99   3.112%   $17.5187   $17.52   $17.50   $17.50  
  Purchase #7 $62.95   8.427%   $68.2548   $68.25   $68.25   $68.30  
  7 purchase totals = $877.90       $945.0248   $945.02   $945.00   $945.10