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 $228.67   5.462%   $241.16   $241.16   $241.15   $241.20  
  Purchase #2 $74.46   4.285%   $77.6506   $77.65   $77.65   $77.70  
  Purchase #3 $153.62   8.596%   $166.8252   $166.83   $166.85   $166.80  
  Purchase #4 $51.35   3.267%   $53.0276   $53.03   $53.05   $53.00  
  Purchase #5 $113.96   11.211%   $126.7361   $126.74   $126.75   $126.70  
  Purchase #6 $159.88   5.515%   $168.6974   $168.70   $168.70   $168.70  
  Purchase #7 $216.65   8.809%   $235.7347   $235.73   $235.75   $235.70  
  7 purchase totals = $998.59       $1,069.8316   $1,069.84   $1,069.90   $1,069.80