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 $67.65   6.743%   $72.2116   $72.21   $72.20   $72.20  
  Purchase #2 $50.31   11.236%   $55.9628   $55.96   $55.95   $56.00  
  Purchase #3 $221.74   11.214%   $246.6059   $246.61   $246.60   $246.60  
  Purchase #4 $131.26   3.867%   $136.3358   $136.34   $136.35   $136.30  
  Purchase #5 $225.68   11.676%   $252.0304   $252.03   $252.05   $252.00  
  Purchase #6 $125.94   7.618%   $135.5341   $135.53   $135.55   $135.50  
  Purchase #7 $77.71   13.102%   $87.8916   $87.89   $87.90   $87.90  
  7 purchase totals = $900.29       $986.5722   $986.57   $986.60   $986.50