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 $225.91   11.228%   $251.2752   $251.28   $251.30   $251.30  
  Purchase #2 $219.53   8.674%   $238.572   $238.57   $238.55   $238.60  
  Purchase #3 $38.25   13.344%   $43.3541   $43.35   $43.35   $43.40  
  Purchase #4 $233.62   4.360%   $243.8058   $243.81   $243.80   $243.80  
  Purchase #5 $111.83   11.748%   $124.9678   $124.97   $124.95   $125.00  
  Purchase #6 $158.25   11.464%   $176.3918   $176.39   $176.40   $176.40  
  Purchase #7 $5.75   4.408%   $6.0035   $6.00   $6.00   $6.00  
  7 purchase totals = $993.14       $1,084.3702   $1,084.37   $1,084.35   $1,084.50