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 $57.96   13.314%   $65.6768   $65.68   $65.70   $65.70  
  Purchase #2 $239.94   11.450%   $267.4131   $267.41   $267.40   $267.40  
  Purchase #3 $176.96   13.327%   $200.5435   $200.54   $200.55   $200.50  
  Purchase #4 $29.61   7.469%   $31.8216   $31.82   $31.80   $31.80  
  Purchase #5 $68.25   7.723%   $73.5209   $73.52   $73.50   $73.50  
  Purchase #6 $69.85   11.734%   $78.0462   $78.05   $78.05   $78.00  
  Purchase #7 $133.53   5.410%   $140.754   $140.75   $140.75   $140.80  
  7 purchase totals = $776.10       $857.7761   $857.77   $857.75   $857.70