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 $226.76   11.217%   $252.1957   $252.20   $252.20   $252.20  
  Purchase #2 $65.81   5.818%   $69.6388   $69.64   $69.65   $69.60  
  Purchase #3 $62.30   9.139%   $67.9936   $67.99   $68.00   $68.00  
  Purchase #4 $75.98   7.613%   $81.7644   $81.76   $81.75   $81.80  
  Purchase #5 $87.94   9.234%   $96.0604   $96.06   $96.05   $96.10  
  Purchase #6 $41.51   7.848%   $44.7677   $44.77   $44.75   $44.80  
  Purchase #7 $131.69   12.408%   $148.0301   $148.03   $148.05   $148.00  
  7 purchase totals = $691.99       $760.4507   $760.45   $760.45   $760.50