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 $241.80   8.813%   $263.1098   $263.11   $263.10   $263.10  
  Purchase #2 $44.26   4.627%   $46.3079   $46.31   $46.30   $46.30  
  Purchase #3 $181.98   3.837%   $188.9626   $188.96   $188.95   $189.00  
  Purchase #4 $72.92   10.253%   $80.3965   $80.40   $80.40   $80.40  
  Purchase #5 $193.94   6.121%   $205.8111   $205.81   $205.80   $205.80  
  Purchase #6 $119.37   12.723%   $134.5574   $134.56   $134.55   $134.60  
  Purchase #7 $119.80   4.296%   $124.9466   $124.95   $124.95   $124.90  
  7 purchase totals = $974.07       $1,044.0919   $1,044.10   $1,044.05   $1,044.10