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 $49.52   10.411%   $54.6755   $54.68   $54.70   $54.70  
  Purchase #2 $196.76   8.232%   $212.9573   $212.96   $212.95   $213.00  
  Purchase #3 $196.70   4.658%   $205.8623   $205.86   $205.85   $205.90  
  Purchase #4 $234.27   3.396%   $242.2258   $242.23   $242.25   $242.20  
  Purchase #5 $31.30   11.699%   $34.9618   $34.96   $34.95   $35.00  
  Purchase #6 $140.45   3.433%   $145.2716   $145.27   $145.25   $145.30  
  Purchase #7 $55.94   12.348%   $62.8475   $62.85   $62.85   $62.80  
  7 purchase totals = $904.94       $958.8018   $958.81   $958.80   $958.90