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 $53.36   11.302%   $59.3907   $59.39   $59.40   $59.40  
  Purchase #2 $212.45   3.344%   $219.5543   $219.55   $219.55   $219.60  
  Purchase #3 $162.46   8.859%   $176.8523   $176.85   $176.85   $176.90  
  Purchase #4 $168.70   5.273%   $177.5956   $177.60   $177.60   $177.60  
  Purchase #5 $95.43   8.255%   $103.3077   $103.31   $103.30   $103.30  
  Purchase #6 $79.69   10.367%   $87.9515   $87.95   $87.95   $88.00  
  Purchase #7 $120.41   8.307%   $130.4125   $130.41   $130.40   $130.40  
  7 purchase totals = $892.50       $955.0646   $955.06   $955.05   $955.20