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 $68.56   9.784%   $75.2679   $75.27   $75.25   $75.30  
  Purchase #2 $173.62   11.499%   $193.5846   $193.58   $193.60   $193.60  
  Purchase #3 $114.32   7.103%   $122.4401   $122.44   $122.45   $122.40  
  Purchase #4 $137.60   7.649%   $148.125   $148.13   $148.15   $148.10  
  Purchase #5 $56.91   4.804%   $59.644   $59.64   $59.65   $59.60  
  Purchase #6 $169.59   13.331%   $192.198   $192.20   $192.20   $192.20  
  Purchase #7 $51.47   9.817%   $56.5228   $56.52   $56.50   $56.50  
  7 purchase totals = $772.07       $847.7824   $847.78   $847.80   $847.70