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 $159.82   13.846%   $181.9487   $181.95   $181.95   $181.90  
  Purchase #2 $96.98   7.797%   $104.5415   $104.54   $104.55   $104.50  
  Purchase #3 $130.34   9.853%   $143.1824   $143.18   $143.20   $143.20  
  Purchase #4 $16.56   6.335%   $17.6091   $17.61   $17.60   $17.60  
  Purchase #5 $220.40   5.710%   $232.9848   $232.98   $233.00   $233.00  
  Purchase #6 $121.51   4.573%   $127.0667   $127.07   $127.05   $127.10  
  Purchase #7 $232.30   13.292%   $263.1773   $263.18   $263.20   $263.20  
  7 purchase totals = $977.91       $1,070.5105   $1,070.51   $1,070.55   $1,070.50