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 $43.41   11.656%   $48.4699   $48.47   $48.45   $48.50  
  Purchase #2 $193.89   5.704%   $204.9495   $204.95   $204.95   $204.90  
  Purchase #3 $137.67   11.191%   $153.0766   $153.08   $153.10   $153.10  
  Purchase #4 $57.70   4.744%   $60.4373   $60.44   $60.45   $60.40  
  Purchase #5 $117.83   5.176%   $123.9289   $123.93   $123.95   $123.90  
  Purchase #6 $226.52   7.723%   $244.0141   $244.01   $244.00   $244.00  
  Purchase #7 $215.51   8.422%   $233.6603   $233.66   $233.65   $233.70  
  7 purchase totals = $992.53       $1,068.5366   $1,068.54   $1,068.55   $1,068.50