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 $115.28   10.621%   $127.5239   $127.52   $127.50   $127.50  
  Purchase #2 $51.81   3.372%   $53.557   $53.56   $53.55   $53.60  
  Purchase #3 $135.62   13.522%   $153.9585   $153.96   $153.95   $154.00  
  Purchase #4 $166.68   5.699%   $176.1791   $176.18   $176.20   $176.20  
  Purchase #5 $231.73   12.380%   $260.4182   $260.42   $260.40   $260.40  
  Purchase #6 $21.79   7.112%   $23.3397   $23.34   $23.35   $23.30  
  Purchase #7 $118.97   10.131%   $131.0229   $131.02   $131.00   $131.00  
  7 purchase totals = $841.88       $925.9993   $926.00   $925.95   $926.00