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 $45.37   5.798%   $48.0006   $48.00   $48.00   $48.00  
  Purchase #2 $218.80   9.570%   $239.7392   $239.74   $239.75   $239.70  
  Purchase #3 $190.69   8.492%   $206.8834   $206.88   $206.90   $206.90  
  Purchase #4 $118.70   5.437%   $125.1537   $125.15   $125.15   $125.20  
  Purchase #5 $65.92   13.454%   $74.7889   $74.79   $74.80   $74.80  
  Purchase #6 $61.41   8.233%   $66.4659   $66.47   $66.45   $66.50  
  Purchase #7 $232.84   5.267%   $245.1037   $245.10   $245.10   $245.10  
  7 purchase totals = $933.73       $1,006.1354   $1,006.13   $1,006.15   $1,006.20