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 $241.68   9.542%   $264.7411   $264.74   $264.75   $264.70  
  Purchase #2 $54.77   3.209%   $56.5276   $56.53   $56.55   $56.50  
  Purchase #3 $180.84   6.695%   $192.9472   $192.95   $192.95   $192.90  
  Purchase #4 $95.35   13.767%   $108.4768   $108.48   $108.50   $108.50  
  Purchase #5 $166.86   8.840%   $181.6104   $181.61   $181.60   $181.60  
  Purchase #6 $32.52   5.158%   $34.1974   $34.20   $34.20   $34.20  
  Purchase #7 $198.91   6.233%   $211.3081   $211.31   $211.30   $211.30  
  7 purchase totals = $970.93       $1,049.8086   $1,049.82   $1,049.85   $1,049.70