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 $225.57   13.155%   $255.2437   $255.24   $255.25   $255.20  
  Purchase #2 $181.27   5.170%   $190.6417   $190.64   $190.65   $190.60  
  Purchase #3 $72.55   4.603%   $75.8895   $75.89   $75.90   $75.90  
  Purchase #4 $173.33   9.563%   $189.9055   $189.91   $189.90   $189.90  
  Purchase #5 $177.51   8.308%   $192.2575   $192.26   $192.25   $192.30  
  Purchase #6 $90.65   4.415%   $94.6522   $94.65   $94.65   $94.70  
  Purchase #7 $28.77   11.211%   $31.9954   $32.00   $32.00   $32.00  
  7 purchase totals = $949.65       $1,030.5855   $1,030.59   $1,030.60   $1,030.60