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 $89.69   6.521%   $95.5387   $95.54   $95.55   $95.50  
  Purchase #2 $183.87   11.570%   $205.1438   $205.14   $205.15   $205.10  
  Purchase #3 $247.46   9.119%   $270.0259   $270.03   $270.05   $270.00  
  Purchase #4 $17.97   3.338%   $18.5698   $18.57   $18.55   $18.60  
  Purchase #5 $134.63   8.294%   $145.7962   $145.80   $145.80   $145.80  
  Purchase #6 $49.31   6.518%   $52.524   $52.52   $52.50   $52.50  
  Purchase #7 $178.52   12.315%   $200.5047   $200.50   $200.50   $200.50  
  7 purchase totals = $901.45       $988.1031   $988.10   $988.10   $988.00