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 $241.94   8.623%   $262.8025   $262.80   $262.80   $262.80  
  Purchase #2 $150.37   9.259%   $164.2928   $164.29   $164.30   $164.30  
  Purchase #3 $39.94   6.310%   $42.4602   $42.46   $42.45   $42.50  
  Purchase #4 $94.34   3.838%   $97.9608   $97.96   $97.95   $98.00  
  Purchase #5 $180.57   11.307%   $200.987   $200.99   $201.00   $201.00  
  Purchase #6 $178.58   5.580%   $188.5448   $188.54   $188.55   $188.50  
  Purchase #7 $43.67   10.678%   $48.3331   $48.33   $48.35   $48.30  
  7 purchase totals = $929.41       $1,005.3812   $1,005.37   $1,005.40   $1,005.40