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 $154.63   11.416%   $172.2826   $172.28   $172.30   $172.30  
  Purchase #2 $211.94   8.820%   $230.6331   $230.63   $230.65   $230.60  
  Purchase #3 $213.86   5.205%   $224.9914   $224.99   $225.00   $225.00  
  Purchase #4 $182.59   12.357%   $205.1526   $205.15   $205.15   $205.20  
  Purchase #5 $56.93   11.341%   $63.3864   $63.39   $63.40   $63.40  
  Purchase #6 $65.50   13.165%   $74.1231   $74.12   $74.10   $74.10  
  Purchase #7 $237.62   11.589%   $265.1578   $265.16   $265.15   $265.20  
  7 purchase totals = $1,123.07       $1,235.7270   $1,235.72   $1,235.75   $1,235.80