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 $235.61   11.399%   $262.4672   $262.47   $262.45   $262.50  
  Purchase #2 $7.34   6.251%   $7.7988   $7.80   $7.80   $7.80  
  Purchase #3 $48.45   8.277%   $52.4602   $52.46   $52.45   $52.50  
  Purchase #4 $59.46   6.190%   $63.1406   $63.14   $63.15   $63.10  
  Purchase #5 $199.76   11.288%   $222.3089   $222.31   $222.30   $222.30  
  Purchase #6 $192.41   8.495%   $208.7552   $208.76   $208.75   $208.80  
  Purchase #7 $181.73   12.372%   $204.2136   $204.21   $204.20   $204.20  
  7 purchase totals = $924.76       $1,021.1445   $1,021.15   $1,021.10   $1,021.20