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 $235.58   7.613%   $253.5147   $253.51   $253.50   $253.50  
  Purchase #2 $67.84   11.135%   $75.394   $75.39   $75.40   $75.40  
  Purchase #3 $77.94   3.658%   $80.791   $80.79   $80.80   $80.80  
  Purchase #4 $53.88   5.155%   $56.6575   $56.66   $56.65   $56.70  
  Purchase #5 $227.48   8.718%   $247.3117   $247.31   $247.30   $247.30  
  Purchase #6 $170.94   6.871%   $182.6853   $182.69   $182.70   $182.70  
  Purchase #7 $73.84   6.559%   $78.6832   $78.68   $78.70   $78.70  
  7 purchase totals = $907.50       $975.0374   $975.03   $975.05   $975.10