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 $245.25   11.603%   $273.7064   $273.71   $273.70   $273.70  
  Purchase #2 $8.59   12.348%   $9.6507   $9.65   $9.65   $9.70  
  Purchase #3 $101.64   11.422%   $113.2493   $113.25   $113.25   $113.20  
  Purchase #4 $26.91   9.390%   $29.4368   $29.44   $29.45   $29.40  
  Purchase #5 $15.71   11.212%   $17.4714   $17.47   $17.45   $17.50  
  Purchase #6 $49.33   13.437%   $55.9585   $55.96   $55.95   $56.00  
  Purchase #7 $184.28   11.546%   $205.557   $205.56   $205.55   $205.60  
  7 purchase totals = $631.71       $705.0301   $705.04   $705.00   $705.10