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 $224.50   9.474%   $245.7691   $245.77   $245.75   $245.80  
  Purchase #2 $68.88   12.137%   $77.24   $77.24   $77.25   $77.20  
  Purchase #3 $150.93   12.858%   $170.3366   $170.34   $170.35   $170.30  
  Purchase #4 $44.40   9.349%   $48.551   $48.55   $48.55   $48.60  
  Purchase #5 $16.94   3.283%   $17.4961   $17.50   $17.50   $17.50  
  Purchase #6 $7.69   9.740%   $8.439   $8.44   $8.45   $8.40  
  Purchase #7 $121.44   4.597%   $127.0226   $127.02   $127.00   $127.00  
  7 purchase totals = $634.78       $694.8544   $694.86   $694.85   $694.80