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 $119.29   5.653%   $126.0335   $126.03   $126.05   $126.00  
  Purchase #2 $50.46   3.751%   $52.3528   $52.35   $52.35   $52.40  
  Purchase #3 $39.85   5.367%   $41.9887   $41.99   $42.00   $42.00  
  Purchase #4 $85.88   5.299%   $90.4308   $90.43   $90.45   $90.40  
  Purchase #5 $94.25   9.708%   $103.3998   $103.40   $103.40   $103.40  
  Purchase #6 $99.94   8.816%   $108.7507   $108.75   $108.75   $108.80  
  Purchase #7 $241.46   10.186%   $266.0551   $266.06   $266.05   $266.10  
  7 purchase totals = $731.13       $789.0114   $789.01   $789.05   $789.10