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 $33.81   4.383%   $35.2919   $35.29   $35.30   $35.30  
  Purchase #2 $85.34   7.378%   $91.6364   $91.64   $91.65   $91.60  
  Purchase #3 $222.40   8.348%   $240.966   $240.97   $240.95   $241.00  
  Purchase #4 $45.54   6.533%   $48.5151   $48.52   $48.50   $48.50  
  Purchase #5 $239.72   11.852%   $268.1316   $268.13   $268.15   $268.10  
  Purchase #6 $100.62   6.243%   $106.9017   $106.90   $106.90   $106.90  
  Purchase #7 $249.62   7.720%   $268.8907   $268.89   $268.90   $268.90  
  7 purchase totals = $977.05       $1,060.3334   $1,060.34   $1,060.35   $1,060.30