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 $57.65   13.681%   $65.5371   $65.54   $65.55   $65.50  
  Purchase #2 $9.97   7.241%   $10.6919   $10.69   $10.70   $10.70  
  Purchase #3 $118.29   6.612%   $126.1113   $126.11   $126.10   $126.10  
  Purchase #4 $136.28   9.844%   $149.6954   $149.70   $149.70   $149.70  
  Purchase #5 $141.39   8.635%   $153.599   $153.60   $153.60   $153.60  
  Purchase #6 $244.97   10.169%   $269.881   $269.88   $269.90   $269.90  
  Purchase #7 $216.46   12.384%   $243.2664   $243.27   $243.25   $243.30  
  7 purchase totals = $925.01       $1,018.7821   $1,018.79   $1,018.80   $1,018.80