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 $73.88   3.598%   $76.5382   $76.54   $76.55   $76.50  
  Purchase #2 $134.71   8.477%   $146.1294   $146.13   $146.15   $146.10  
  Purchase #3 $138.50   10.775%   $153.4234   $153.42   $153.40   $153.40  
  Purchase #4 $241.31   11.481%   $269.0148   $269.01   $269.00   $269.00  
  Purchase #5 $160.36   8.200%   $173.5095   $173.51   $173.50   $173.50  
  Purchase #6 $7.45   8.226%   $8.0628   $8.06   $8.05   $8.10  
  Purchase #7 $127.44   6.736%   $136.0244   $136.02   $136.00   $136.00  
  7 purchase totals = $883.65       $962.7025   $962.69   $962.65   $962.60