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 $163.64   3.746%   $169.77   $169.77   $169.75   $169.80  
  Purchase #2 $42.79   5.226%   $45.0262   $45.03   $45.05   $45.00  
  Purchase #3 $177.26   8.489%   $192.3076   $192.31   $192.30   $192.30  
  Purchase #4 $236.81   9.546%   $259.4159   $259.42   $259.40   $259.40  
  Purchase #5 $208.30   11.791%   $232.8607   $232.86   $232.85   $232.90  
  Purchase #6 $227.99   10.379%   $251.6531   $251.65   $251.65   $251.70  
  Purchase #7 $168.68   8.204%   $182.5185   $182.52   $182.50   $182.50  
  7 purchase totals = $1,225.47       $1,333.5520   $1,333.56   $1,333.50   $1,333.60