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 $184.92   8.534%   $200.7011   $200.70   $200.70   $200.70  
  Purchase #2 $250.66   8.339%   $271.5625   $271.56   $271.55   $271.60  
  Purchase #3 $53.77   11.296%   $59.8439   $59.84   $59.85   $59.80  
  Purchase #4 $250.73   4.794%   $262.75   $262.75   $262.75   $262.80  
  Purchase #5 $160.91   5.718%   $170.1108   $170.11   $170.10   $170.10  
  Purchase #6 $87.69   9.810%   $96.2924   $96.29   $96.30   $96.30  
  Purchase #7 $51.93   5.217%   $54.6392   $54.64   $54.65   $54.60  
  7 purchase totals = $1,040.61       $1,115.8999   $1,115.89   $1,115.90   $1,115.90