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 $55.81   12.251%   $62.6473   $62.65   $62.65   $62.60  
  Purchase #2 $190.88   3.711%   $197.9636   $197.96   $197.95   $198.00  
  Purchase #3 $137.99   12.349%   $155.0304   $155.03   $155.05   $155.00  
  Purchase #4 $134.27   9.683%   $147.2714   $147.27   $147.25   $147.30  
  Purchase #5 $58.67   3.503%   $60.7252   $60.73   $60.75   $60.70  
  Purchase #6 $109.42   12.108%   $122.6686   $122.67   $122.65   $122.70  
  Purchase #7 $22.73   8.286%   $24.6134   $24.61   $24.60   $24.60  
  7 purchase totals = $709.77       $770.9199   $770.92   $770.90   $770.90