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 $64.55   7.795%   $69.5817   $69.58   $69.60   $69.60  
  Purchase #2 $206.76   6.812%   $220.8445   $220.84   $220.85   $220.80  
  Purchase #3 $69.47   12.481%   $78.1406   $78.14   $78.15   $78.10  
  Purchase #4 $108.26   8.828%   $117.8172   $117.82   $117.80   $117.80  
  Purchase #5 $164.52   11.758%   $183.8643   $183.86   $183.85   $183.90  
  Purchase #6 $152.48   4.558%   $159.43   $159.43   $159.45   $159.40  
  Purchase #7 $15.93   6.530%   $16.9702   $16.97   $16.95   $17.00  
  7 purchase totals = $781.97       $846.6485   $846.64   $846.65   $846.60