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 $52.81   13.629%   $60.0075   $60.01   $60.00   $60.00  
  Purchase #2 $34.29   6.849%   $36.6385   $36.64   $36.65   $36.60  
  Purchase #3 $111.40   4.652%   $116.5823   $116.58   $116.60   $116.60  
  Purchase #4 $156.26   13.376%   $177.1613   $177.16   $177.15   $177.20  
  Purchase #5 $183.55   7.559%   $197.4245   $197.42   $197.40   $197.40  
  Purchase #6 $220.30   9.204%   $240.5764   $240.58   $240.60   $240.60  
  Purchase #7 $212.68   9.339%   $232.5422   $232.54   $232.55   $232.50  
  7 purchase totals = $971.29       $1,060.9327   $1,060.93   $1,060.95   $1,060.90