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 $223.25   3.459%   $230.9722   $230.97   $230.95   $231.00  
  Purchase #2 $215.34   5.286%   $226.7229   $226.72   $226.70   $226.70  
  Purchase #3 $30.29   3.393%   $31.3177   $31.32   $31.30   $31.30  
  Purchase #4 $12.46   9.696%   $13.6681   $13.67   $13.65   $13.70  
  Purchase #5 $60.54   8.102%   $65.445   $65.45   $65.45   $65.40  
  Purchase #6 $150.47   11.266%   $167.422   $167.42   $167.40   $167.40  
  Purchase #7 $207.29   3.594%   $214.74   $214.74   $214.75   $214.70  
  7 purchase totals = $899.64       $950.2879   $950.29   $950.20   $950.20