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 $90.54   4.519%   $94.6315   $94.63   $94.65   $94.60  
  Purchase #2 $147.74   10.772%   $163.6546   $163.65   $163.65   $163.70  
  Purchase #3 $219.80   3.409%   $227.293   $227.29   $227.30   $227.30  
  Purchase #4 $20.75   5.275%   $21.8446   $21.84   $21.85   $21.80  
  Purchase #5 $246.47   9.397%   $269.6308   $269.63   $269.65   $269.60  
  Purchase #6 $52.60   3.669%   $54.5299   $54.53   $54.55   $54.50  
  Purchase #7 $211.41   4.671%   $221.285   $221.29   $221.30   $221.30  
  7 purchase totals = $989.31       $1,052.8694   $1,052.86   $1,052.95   $1,052.80