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 $106.68   11.684%   $119.1445   $119.14   $119.15   $119.10  
  Purchase #2 $168.77   5.123%   $177.4161   $177.42   $177.40   $177.40  
  Purchase #3 $236.61   7.422%   $254.1712   $254.17   $254.15   $254.20  
  Purchase #4 $154.73   3.426%   $160.031   $160.03   $160.05   $160.00  
  Purchase #5 $111.54   9.865%   $122.5434   $122.54   $122.55   $122.50  
  Purchase #6 $9.36   3.684%   $9.7048   $9.70   $9.70   $9.70  
  Purchase #7 $73.59   7.286%   $78.9518   $78.95   $78.95   $79.00  
  7 purchase totals = $861.28       $921.9628   $921.95   $921.95   $921.90