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 $93.48   3.685%   $96.9247   $96.92   $96.90   $96.90  
  Purchase #2 $197.52   8.563%   $214.4336   $214.43   $214.45   $214.40  
  Purchase #3 $120.97   11.327%   $134.6723   $134.67   $134.65   $134.70  
  Purchase #4 $85.76   13.726%   $97.5314   $97.53   $97.55   $97.50  
  Purchase #5 $228.71   12.380%   $257.0243   $257.02   $257.00   $257.00  
  Purchase #6 $246.72   9.337%   $269.7562   $269.76   $269.75   $269.80  
  Purchase #7 $229.54   5.219%   $241.5197   $241.52   $241.50   $241.50  
  7 purchase totals = $1,202.70       $1,311.8622   $1,311.85   $1,311.80   $1,311.80