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 $163.52   10.691%   $181.0019   $181.00   $181.00   $181.00  
  Purchase #2 $30.87   8.369%   $33.4535   $33.45   $33.45   $33.50  
  Purchase #3 $168.94   11.841%   $188.9442   $188.94   $188.95   $188.90  
  Purchase #4 $154.64   3.131%   $159.4818   $159.48   $159.50   $159.50  
  Purchase #5 $117.32   5.493%   $123.7644   $123.76   $123.75   $123.80  
  Purchase #6 $246.54   8.664%   $267.9002   $267.90   $267.90   $267.90  
  Purchase #7 $225.57   11.360%   $251.1948   $251.19   $251.20   $251.20  
  7 purchase totals = $1,107.40       $1,205.7408   $1,205.72   $1,205.75   $1,205.80