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 $244.50   7.802%   $263.5759   $263.58   $263.60   $263.60  
  Purchase #2 $130.98   6.529%   $139.5317   $139.53   $139.55   $139.50  
  Purchase #3 $139.78   12.158%   $156.7745   $156.77   $156.75   $156.80  
  Purchase #4 $68.96   6.610%   $73.5183   $73.52   $73.50   $73.50  
  Purchase #5 $122.87   8.141%   $132.8728   $132.87   $132.85   $132.90  
  Purchase #6 $121.36   8.577%   $131.769   $131.77   $131.75   $131.80  
  Purchase #7 $71.67   10.716%   $79.3502   $79.35   $79.35   $79.40  
  7 purchase totals = $900.12       $977.3924   $977.39   $977.35   $977.50