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 $53.68   7.298%   $57.5976   $57.60   $57.60   $57.60  
  Purchase #2 $99.28   9.488%   $108.6997   $108.70   $108.70   $108.70  
  Purchase #3 $87.36   8.703%   $94.9629   $94.96   $94.95   $95.00  
  Purchase #4 $192.84   12.278%   $216.5169   $216.52   $216.50   $216.50  
  Purchase #5 $115.45   6.362%   $122.7949   $122.79   $122.80   $122.80  
  Purchase #6 $175.62   12.416%   $197.425   $197.43   $197.45   $197.40  
  Purchase #7 $169.92   5.602%   $179.4389   $179.44   $179.45   $179.40  
  7 purchase totals = $894.15       $977.4359   $977.44   $977.45   $977.40