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 $235.28   4.833%   $246.6511   $246.65   $246.65   $246.70  
  Purchase #2 $55.45   7.467%   $59.5905   $59.59   $59.60   $59.60  
  Purchase #3 $173.85   12.246%   $195.1397   $195.14   $195.15   $195.10  
  Purchase #4 $228.64   8.194%   $247.3748   $247.37   $247.35   $247.40  
  Purchase #5 $210.85   13.680%   $239.6943   $239.69   $239.70   $239.70  
  Purchase #6 $195.37   11.597%   $218.0271   $218.03   $218.05   $218.00  
  Purchase #7 $58.94   6.816%   $62.9574   $62.96   $62.95   $63.00  
  7 purchase totals = $1,158.38       $1,269.4349   $1,269.43   $1,269.45   $1,269.50