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 $119.80   12.369%   $134.6181   $134.62   $134.60   $134.60  
  Purchase #2 $58.86   10.382%   $64.9708   $64.97   $64.95   $65.00  
  Purchase #3 $204.79   10.837%   $226.9831   $226.98   $227.00   $227.00  
  Purchase #4 $208.46   3.428%   $215.606   $215.61   $215.60   $215.60  
  Purchase #5 $167.32   11.338%   $186.2907   $186.29   $186.30   $186.30  
  Purchase #6 $38.80   11.714%   $43.345   $43.35   $43.35   $43.30  
  Purchase #7 $211.91   5.446%   $223.4506   $223.45   $223.45   $223.50  
  7 purchase totals = $1,009.94       $1,095.2643   $1,095.27   $1,095.25   $1,095.30