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 $192.46   7.402%   $206.7059   $206.71   $206.70   $206.70  
  Purchase #2 $13.70   4.215%   $14.2775   $14.28   $14.30   $14.30  
  Purchase #3 $36.28   9.539%   $39.7407   $39.74   $39.75   $39.70  
  Purchase #4 $236.26   9.261%   $258.14   $258.14   $258.15   $258.10  
  Purchase #5 $217.55   11.349%   $242.2397   $242.24   $242.25   $242.20  
  Purchase #6 $145.26   11.157%   $161.4667   $161.47   $161.45   $161.50  
  Purchase #7 $55.46   9.607%   $60.788   $60.79   $60.80   $60.80  
  7 purchase totals = $896.97       $983.3585   $983.37   $983.40   $983.30