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 $48.55   8.324%   $52.5913   $52.59   $52.60   $52.60  
  Purchase #2 $182.87   7.682%   $196.9181   $196.92   $196.90   $196.90  
  Purchase #3 $121.71   4.107%   $126.7086   $126.71   $126.70   $126.70  
  Purchase #4 $153.48   11.674%   $171.3973   $171.40   $171.40   $171.40  
  Purchase #5 $96.99   12.843%   $109.4464   $109.45   $109.45   $109.40  
  Purchase #6 $119.50   9.392%   $130.7234   $130.72   $130.70   $130.70  
  Purchase #7 $151.33   6.376%   $160.9788   $160.98   $161.00   $161.00  
  7 purchase totals = $874.43       $948.7639   $948.77   $948.75   $948.70