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 $32.42   5.647%   $34.2508   $34.25   $34.25   $34.30  
  Purchase #2 $106.78   3.814%   $110.8526   $110.85   $110.85   $110.90  
  Purchase #3 $212.75   10.378%   $234.8292   $234.83   $234.85   $234.80  
  Purchase #4 $241.89   5.846%   $256.0309   $256.03   $256.05   $256.00  
  Purchase #5 $33.69   12.695%   $37.9669   $37.97   $37.95   $38.00  
  Purchase #6 $45.65   10.688%   $50.5291   $50.53   $50.55   $50.50  
  Purchase #7 $9.55   3.389%   $9.8736   $9.87   $9.85   $9.90  
  7 purchase totals = $682.73       $734.3331   $734.33   $734.35   $734.40