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 $33.65   7.697%   $36.24   $36.24   $36.25   $36.20  
  Purchase #2 $121.83   5.580%   $128.6281   $128.63   $128.65   $128.60  
  Purchase #3 $20.94   9.426%   $22.9138   $22.91   $22.90   $22.90  
  Purchase #4 $204.81   6.418%   $217.9547   $217.95   $217.95   $218.00  
  Purchase #5 $212.59   13.132%   $240.5073   $240.51   $240.50   $240.50  
  Purchase #6 $220.27   4.395%   $229.9509   $229.95   $229.95   $230.00  
  Purchase #7 $167.77   11.287%   $186.7062   $186.71   $186.70   $186.70  
  7 purchase totals = $981.86       $1,062.9010   $1,062.90   $1,062.90   $1,062.90