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 $81.81   13.674%   $92.9967   $93.00   $93.00   $93.00  
  Purchase #2 $52.85   4.583%   $55.2721   $55.27   $55.25   $55.30  
  Purchase #3 $196.59   3.739%   $203.9405   $203.94   $203.95   $203.90  
  Purchase #4 $201.78   8.219%   $218.3643   $218.36   $218.35   $218.40  
  Purchase #5 $186.99   10.458%   $206.5454   $206.55   $206.55   $206.50  
  Purchase #6 $218.48   8.533%   $237.1229   $237.12   $237.10   $237.10  
  Purchase #7 $50.59   8.201%   $54.7389   $54.74   $54.75   $54.70  
  7 purchase totals = $989.09       $1,068.9808   $1,068.98   $1,068.95   $1,068.90