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 $59.55   6.453%   $63.3928   $63.39   $63.40   $63.40  
  Purchase #2 $71.81   8.650%   $78.0216   $78.02   $78.00   $78.00  
  Purchase #3 $179.57   7.820%   $193.6124   $193.61   $193.60   $193.60  
  Purchase #4 $190.84   11.228%   $212.2675   $212.27   $212.25   $212.30  
  Purchase #5 $137.32   11.368%   $152.9305   $152.93   $152.95   $152.90  
  Purchase #6 $192.62   6.527%   $205.1923   $205.19   $205.20   $205.20  
  Purchase #7 $130.82   5.309%   $137.7652   $137.77   $137.75   $137.80  
  7 purchase totals = $962.53       $1,043.1823   $1,043.18   $1,043.15   $1,043.20