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 $103.95   11.473%   $115.8762   $115.88   $115.90   $115.90  
  Purchase #2 $222.86   9.295%   $243.5748   $243.57   $243.55   $243.60  
  Purchase #3 $28.59   8.398%   $30.991   $30.99   $31.00   $31.00  
  Purchase #4 $40.41   11.746%   $45.1566   $45.16   $45.15   $45.20  
  Purchase #5 $224.58   8.156%   $242.8967   $242.90   $242.90   $242.90  
  Purchase #6 $232.60   3.862%   $241.583   $241.58   $241.60   $241.60  
  Purchase #7 $96.78   8.491%   $104.9976   $105.00   $105.00   $105.00  
  7 purchase totals = $949.77       $1,025.0759   $1,025.08   $1,025.10   $1,025.20