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 $224.79   11.661%   $251.0028   $251.00   $251.00   $251.00  
  Purchase #2 $184.84   4.369%   $192.9157   $192.92   $192.90   $192.90  
  Purchase #3 $32.53   9.449%   $35.6038   $35.60   $35.60   $35.60  
  Purchase #4 $102.49   10.689%   $113.4452   $113.45   $113.45   $113.40  
  Purchase #5 $173.60   6.742%   $185.3041   $185.30   $185.30   $185.30  
  Purchase #6 $230.69   12.199%   $258.8319   $258.83   $258.85   $258.80  
  Purchase #7 $59.61   8.491%   $64.6715   $64.67   $64.65   $64.70  
  7 purchase totals = $1,008.55       $1,101.7750   $1,101.77   $1,101.75   $1,101.70