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 $58.32   11.490%   $65.021   $65.02   $65.00   $65.00  
  Purchase #2 $47.78   8.779%   $51.9746   $51.97   $51.95   $52.00  
  Purchase #3 $91.34   8.384%   $98.9979   $99.00   $99.00   $99.00  
  Purchase #4 $77.25   12.232%   $86.6992   $86.70   $86.70   $86.70  
  Purchase #5 $108.62   4.627%   $113.6458   $113.65   $113.65   $113.60  
  Purchase #6 $225.98   6.421%   $240.4902   $240.49   $240.50   $240.50  
  Purchase #7 $49.34   10.120%   $54.3332   $54.33   $54.35   $54.30  
  7 purchase totals = $658.63       $711.1619   $711.16   $711.15   $711.10