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 $59.44   3.353%   $61.433   $61.43   $61.45   $61.40  
  Purchase #2 $246.48   4.108%   $256.6054   $256.61   $256.60   $256.60  
  Purchase #3 $207.43   7.344%   $222.6637   $222.66   $222.65   $222.70  
  Purchase #4 $62.87   12.444%   $70.6935   $70.69   $70.70   $70.70  
  Purchase #5 $211.94   3.325%   $218.987   $218.99   $219.00   $219.00  
  Purchase #6 $11.64   13.586%   $13.2214   $13.22   $13.20   $13.20  
  Purchase #7 $132.27   9.632%   $145.0102   $145.01   $145.00   $145.00  
  7 purchase totals = $932.07       $988.6142   $988.61   $988.60   $988.60