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 $244.49   11.577%   $272.7946   $272.79   $272.80   $272.80  
  Purchase #2 $208.58   8.831%   $226.9997   $227.00   $227.00   $227.00  
  Purchase #3 $54.63   9.560%   $59.8526   $59.85   $59.85   $59.90  
  Purchase #4 $220.91   5.169%   $232.3288   $232.33   $232.35   $232.30  
  Purchase #5 $57.37   5.768%   $60.6791   $60.68   $60.70   $60.70  
  Purchase #6 $57.39   5.673%   $60.6457   $60.65   $60.65   $60.60  
  Purchase #7 $226.32   3.673%   $234.6327   $234.63   $234.65   $234.60  
  7 purchase totals = $1,069.69       $1,147.9332   $1,147.93   $1,148.00   $1,147.90