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 $237.51   5.294%   $250.0838   $250.08   $250.10   $250.10  
  Purchase #2 $9.30   3.229%   $9.6003   $9.60   $9.60   $9.60  
  Purchase #3 $40.90   6.570%   $43.5871   $43.59   $43.60   $43.60  
  Purchase #4 $192.49   5.349%   $202.7863   $202.79   $202.80   $202.80  
  Purchase #5 $148.26   3.160%   $152.945   $152.95   $152.95   $152.90  
  Purchase #6 $149.61   3.598%   $154.993   $154.99   $155.00   $155.00  
  Purchase #7 $158.43   13.861%   $180.39   $180.39   $180.40   $180.40  
  7 purchase totals = $936.50       $994.3855   $994.39   $994.45   $994.40