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 $186.90   13.368%   $211.8848   $211.88   $211.90   $211.90  
  Purchase #2 $17.81   8.261%   $19.2813   $19.28   $19.30   $19.30  
  Purchase #3 $206.52   13.783%   $234.9847   $234.98   $235.00   $235.00  
  Purchase #4 $49.68   11.182%   $55.2352   $55.24   $55.25   $55.20  
  Purchase #5 $183.50   6.672%   $195.7431   $195.74   $195.75   $195.70  
  Purchase #6 $166.93   11.386%   $185.9366   $185.94   $185.95   $185.90  
  Purchase #7 $172.61   6.683%   $184.1455   $184.15   $184.15   $184.10  
  7 purchase totals = $983.95       $1,087.2112   $1,087.21   $1,087.30   $1,087.10