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 $59.27   3.200%   $61.1666   $61.17   $61.15   $61.20  
  Purchase #2 $69.55   3.303%   $71.8472   $71.85   $71.85   $71.80  
  Purchase #3 $218.42   6.716%   $233.0891   $233.09   $233.10   $233.10  
  Purchase #4 $72.34   3.182%   $74.6419   $74.64   $74.65   $74.60  
  Purchase #5 $125.40   12.450%   $141.0123   $141.01   $141.00   $141.00  
  Purchase #6 $232.86   6.650%   $248.3452   $248.35   $248.35   $248.30  
  Purchase #7 $19.50   13.757%   $22.1826   $22.18   $22.20   $22.20  
  7 purchase totals = $797.34       $852.2849   $852.29   $852.30   $852.20