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 $115.75   9.752%   $127.0379   $127.04   $127.05   $127.00  
  Purchase #2 $199.94   5.519%   $210.9747   $210.97   $210.95   $211.00  
  Purchase #3 $173.78   4.549%   $181.6853   $181.69   $181.70   $181.70  
  Purchase #4 $192.57   4.219%   $200.6945   $200.69   $200.70   $200.70  
  Purchase #5 $169.73   8.746%   $184.5746   $184.57   $184.55   $184.60  
  Purchase #6 $19.26   11.319%   $21.44   $21.44   $21.45   $21.40  
  Purchase #7 $115.28   6.195%   $122.4216   $122.42   $122.40   $122.40  
  7 purchase totals = $986.31       $1,048.8286   $1,048.82   $1,048.80   $1,048.80