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 $119.83   11.836%   $134.0131   $134.01   $134.00   $134.00  
  Purchase #2 $177.79   13.806%   $202.3357   $202.34   $202.35   $202.30  
  Purchase #3 $49.40   12.740%   $55.6936   $55.69   $55.70   $55.70  
  Purchase #4 $185.87   8.293%   $201.2842   $201.28   $201.30   $201.30  
  Purchase #5 $82.66   10.242%   $91.126   $91.13   $91.15   $91.10  
  Purchase #6 $15.81   9.628%   $17.3322   $17.33   $17.35   $17.30  
  Purchase #7 $181.63   10.869%   $201.3714   $201.37   $201.35   $201.40  
  7 purchase totals = $812.99       $903.1562   $903.15   $903.20   $903.10