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 $48.96   5.817%   $51.808   $51.81   $51.80   $51.80  
  Purchase #2 $87.96   12.420%   $98.8846   $98.88   $98.90   $98.90  
  Purchase #3 $165.59   3.838%   $171.9453   $171.95   $171.95   $171.90  
  Purchase #4 $247.67   7.241%   $265.6038   $265.60   $265.60   $265.60  
  Purchase #5 $206.44   10.218%   $227.534   $227.53   $227.55   $227.50  
  Purchase #6 $80.82   8.410%   $87.617   $87.62   $87.60   $87.60  
  Purchase #7 $145.88   6.783%   $155.775   $155.78   $155.80   $155.80  
  7 purchase totals = $983.32       $1,059.1677   $1,059.17   $1,059.20   $1,059.10