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 $56.39   6.336%   $59.9629   $59.96   $59.95   $60.00  
  Purchase #2 $83.52   3.270%   $86.2511   $86.25   $86.25   $86.30  
  Purchase #3 $106.80   12.417%   $120.0614   $120.06   $120.05   $120.10  
  Purchase #4 $244.47   10.183%   $269.3644   $269.36   $269.35   $269.40  
  Purchase #5 $169.77   7.802%   $183.0155   $183.02   $183.00   $183.00  
  Purchase #6 $128.43   3.684%   $133.1614   $133.16   $133.15   $133.20  
  Purchase #7 $65.79   7.555%   $70.7604   $70.76   $70.75   $70.80  
  7 purchase totals = $855.17       $922.5771   $922.57   $922.50   $922.80