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 $46.99   13.280%   $53.2303   $53.23   $53.25   $53.20  
  Purchase #2 $44.96   7.341%   $48.2605   $48.26   $48.25   $48.30  
  Purchase #3 $220.92   6.387%   $235.0302   $235.03   $235.05   $235.00  
  Purchase #4 $73.71   12.498%   $82.9223   $82.92   $82.90   $82.90  
  Purchase #5 $91.77   7.531%   $98.6812   $98.68   $98.70   $98.70  
  Purchase #6 $235.40   7.208%   $252.3676   $252.37   $252.35   $252.40  
  Purchase #7 $167.56   9.288%   $183.123   $183.12   $183.10   $183.10  
  7 purchase totals = $881.31       $953.6151   $953.61   $953.60   $953.60