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 $162.94   3.856%   $169.223   $169.22   $169.20   $169.20  
  Purchase #2 $64.93   5.524%   $68.5167   $68.52   $68.50   $68.50  
  Purchase #3 $66.56   6.397%   $70.8178   $70.82   $70.80   $70.80  
  Purchase #4 $64.91   9.835%   $71.2939   $71.29   $71.30   $71.30  
  Purchase #5 $46.92   10.114%   $51.6655   $51.67   $51.65   $51.70  
  Purchase #6 $168.37   7.644%   $181.2402   $181.24   $181.25   $181.20  
  Purchase #7 $163.93   10.416%   $181.0049   $181.00   $181.00   $181.00  
  7 purchase totals = $738.56       $793.7620   $793.76   $793.70   $793.70