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 $58.93   13.687%   $66.9957   $67.00   $67.00   $67.00  
  Purchase #2 $192.57   9.670%   $211.1915   $211.19   $211.20   $211.20  
  Purchase #3 $101.83   8.407%   $110.3908   $110.39   $110.40   $110.40  
  Purchase #4 $130.65   9.441%   $142.9847   $142.98   $143.00   $143.00  
  Purchase #5 $101.75   9.519%   $111.4356   $111.44   $111.45   $111.40  
  Purchase #6 $26.75   4.558%   $27.9693   $27.97   $27.95   $28.00  
  Purchase #7 $110.68   5.718%   $117.0087   $117.01   $117.00   $117.00  
  7 purchase totals = $723.16       $787.9763   $787.98   $788.00   $788.00