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 $59.44   6.501%   $63.3042   $63.30   $63.30   $63.30  
  Purchase #2 $222.54   9.519%   $243.7236   $243.72   $243.70   $243.70  
  Purchase #3 $25.77   10.123%   $28.3787   $28.38   $28.40   $28.40  
  Purchase #4 $161.46   10.107%   $177.7788   $177.78   $177.80   $177.80  
  Purchase #5 $209.63   13.211%   $237.3242   $237.32   $237.30   $237.30  
  Purchase #6 $151.83   10.868%   $168.3309   $168.33   $168.35   $168.30  
  Purchase #7 $145.91   11.813%   $163.1463   $163.15   $163.15   $163.10  
  7 purchase totals = $976.58       $1,081.9867   $1,081.98   $1,082.00   $1,081.90