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 $22.52   6.441%   $23.9705   $23.97   $23.95   $24.00  
  Purchase #2 $19.33   12.610%   $21.7675   $21.77   $21.75   $21.80  
  Purchase #3 $185.39   5.751%   $196.0518   $196.05   $196.05   $196.10  
  Purchase #4 $58.72   6.344%   $62.4452   $62.45   $62.45   $62.40  
  Purchase #5 $81.33   7.320%   $87.2834   $87.28   $87.30   $87.30  
  Purchase #6 $95.58   4.626%   $100.0015   $100.00   $100.00   $100.00  
  Purchase #7 $117.53   6.387%   $125.0366   $125.04   $125.05   $125.00  
  7 purchase totals = $580.40       $616.5565   $616.56   $616.55   $616.60