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 $231.96   6.384%   $246.7683   $246.77   $246.75   $246.80  
  Purchase #2 $92.78   4.433%   $96.8929   $96.89   $96.90   $96.90  
  Purchase #3 $60.61   7.248%   $65.003   $65.00   $65.00   $65.00  
  Purchase #4 $123.29   5.482%   $130.0488   $130.05   $130.05   $130.00  
  Purchase #5 $213.87   10.654%   $236.6557   $236.66   $236.65   $236.70  
  Purchase #6 $64.59   4.220%   $67.3157   $67.32   $67.30   $67.30  
  Purchase #7 $32.45   7.135%   $34.7653   $34.77   $34.75   $34.80  
  7 purchase totals = $819.55       $877.4497   $877.46   $877.40   $877.50