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 $181.88   11.776%   $203.2982   $203.30   $203.30   $203.30  
  Purchase #2 $123.72   5.771%   $130.8599   $130.86   $130.85   $130.90  
  Purchase #3 $18.38   12.671%   $20.7089   $20.71   $20.70   $20.70  
  Purchase #4 $77.52   6.523%   $82.5766   $82.58   $82.60   $82.60  
  Purchase #5 $21.72   3.474%   $22.4746   $22.47   $22.45   $22.50  
  Purchase #6 $222.96   11.774%   $249.2113   $249.21   $249.20   $249.20  
  Purchase #7 $229.83   12.270%   $258.0301   $258.03   $258.05   $258.00  
  7 purchase totals = $876.01       $967.1596   $967.16   $967.15   $967.20