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 $50.33   11.723%   $56.2302   $56.23   $56.25   $56.20  
  Purchase #2 $213.41   13.846%   $242.9587   $242.96   $242.95   $243.00  
  Purchase #3 $119.93   5.274%   $126.2551   $126.26   $126.25   $126.30  
  Purchase #4 $135.89   7.344%   $145.8698   $145.87   $145.85   $145.90  
  Purchase #5 $75.76   6.753%   $80.8761   $80.88   $80.90   $80.90  
  Purchase #6 $39.80   9.653%   $43.6419   $43.64   $43.65   $43.60  
  Purchase #7 $165.71   13.424%   $187.9549   $187.95   $187.95   $188.00  
  7 purchase totals = $800.83       $883.7867   $883.79   $883.80   $883.90