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 $63.61   9.591%   $69.7108   $69.71   $69.70   $69.70  
  Purchase #2 $180.84   12.428%   $203.3148   $203.31   $203.30   $203.30  
  Purchase #3 $132.66   7.477%   $142.579   $142.58   $142.60   $142.60  
  Purchase #4 $153.53   12.469%   $172.6737   $172.67   $172.65   $172.70  
  Purchase #5 $114.40   10.623%   $126.5527   $126.55   $126.55   $126.60  
  Purchase #6 $51.90   11.841%   $58.0455   $58.05   $58.05   $58.00  
  Purchase #7 $244.28   6.746%   $260.7591   $260.76   $260.75   $260.80  
  7 purchase totals = $941.22       $1,033.6356   $1,033.63   $1,033.60   $1,033.70