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 $52.72   13.344%   $59.755   $59.76   $59.75   $59.80  
  Purchase #2 $101.89   4.280%   $106.2509   $106.25   $106.25   $106.30  
  Purchase #3 $55.49   13.505%   $62.9839   $62.98   $63.00   $63.00  
  Purchase #4 $216.35   8.154%   $233.9912   $233.99   $234.00   $234.00  
  Purchase #5 $191.30   10.353%   $211.1053   $211.11   $211.10   $211.10  
  Purchase #6 $144.99   8.171%   $156.8371   $156.84   $156.85   $156.80  
  Purchase #7 $34.72   11.784%   $38.8114   $38.81   $38.80   $38.80  
  7 purchase totals = $797.46       $869.7348   $869.74   $869.75   $869.80