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 $98.71   10.360%   $108.9364   $108.94   $108.95   $108.90  
  Purchase #2 $135.93   12.308%   $152.6603   $152.66   $152.65   $152.70  
  Purchase #3 $66.31   8.519%   $71.9589   $71.96   $71.95   $72.00  
  Purchase #4 $112.99   12.650%   $127.2832   $127.28   $127.30   $127.30  
  Purchase #5 $216.86   8.198%   $234.6382   $234.64   $234.65   $234.60  
  Purchase #6 $203.44   11.156%   $226.1358   $226.14   $226.15   $226.10  
  Purchase #7 $83.48   11.190%   $92.8214   $92.82   $92.80   $92.80  
  7 purchase totals = $917.72       $1,014.4342   $1,014.44   $1,014.45   $1,014.40