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 $53.71   9.553%   $58.8409   $58.84   $58.85   $58.80  
  Purchase #2 $24.86   3.247%   $25.6672   $25.67   $25.65   $25.70  
  Purchase #3 $230.93   9.140%   $252.037   $252.04   $252.05   $252.00  
  Purchase #4 $31.57   4.772%   $33.0765   $33.08   $33.10   $33.10  
  Purchase #5 $235.42   3.588%   $243.8669   $243.87   $243.85   $243.90  
  Purchase #6 $117.83   7.355%   $126.4964   $126.50   $126.50   $126.50  
  Purchase #7 $202.46   12.497%   $227.7614   $227.76   $227.75   $227.80  
  7 purchase totals = $896.78       $967.7463   $967.76   $967.75   $967.80