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 $61.28   12.296%   $68.815   $68.82   $68.80   $68.80  
  Purchase #2 $43.61   5.246%   $45.8978   $45.90   $45.90   $45.90  
  Purchase #3 $111.72   13.786%   $127.1217   $127.12   $127.10   $127.10  
  Purchase #4 $244.67   12.873%   $276.1664   $276.17   $276.15   $276.20  
  Purchase #5 $139.43   12.585%   $156.9773   $156.98   $157.00   $157.00  
  Purchase #6 $145.67   5.670%   $153.9295   $153.93   $153.95   $153.90  
  Purchase #7 $60.76   6.757%   $64.8656   $64.87   $64.85   $64.90  
  7 purchase totals = $807.14       $893.7733   $893.79   $893.75   $893.80