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 $63.98   11.187%   $71.1374   $71.14   $71.15   $71.10  
  Purchase #2 $222.91   7.184%   $238.9239   $238.92   $238.90   $238.90  
  Purchase #3 $207.29   9.404%   $226.7836   $226.78   $226.80   $226.80  
  Purchase #4 $199.48   11.373%   $222.1669   $222.17   $222.15   $222.20  
  Purchase #5 $69.30   10.187%   $76.3596   $76.36   $76.35   $76.40  
  Purchase #6 $25.27   11.352%   $28.1387   $28.14   $28.15   $28.10  
  Purchase #7 $208.26   5.705%   $220.1412   $220.14   $220.15   $220.10  
  7 purchase totals = $996.49       $1,083.6513   $1,083.65   $1,083.65   $1,083.60