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 $56.55   12.611%   $63.6815   $63.68   $63.70   $63.70  
  Purchase #2 $241.34   5.256%   $254.0248   $254.02   $254.00   $254.00  
  Purchase #3 $248.83   5.263%   $261.9259   $261.93   $261.95   $261.90  
  Purchase #4 $221.81   8.323%   $240.2712   $240.27   $240.25   $240.30  
  Purchase #5 $93.75   12.202%   $105.1894   $105.19   $105.20   $105.20  
  Purchase #6 $25.73   7.505%   $27.661   $27.66   $27.65   $27.70  
  Purchase #7 $52.85   3.307%   $54.5977   $54.60   $54.60   $54.60  
  7 purchase totals = $940.86       $1,007.3515   $1,007.35   $1,007.35   $1,007.40