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 $246.95   12.268%   $277.2458   $277.25   $277.25   $277.20  
  Purchase #2 $245.81   12.631%   $276.8583   $276.86   $276.85   $276.90  
  Purchase #3 $104.39   6.293%   $110.9593   $110.96   $110.95   $111.00  
  Purchase #4 $92.58   8.449%   $100.4021   $100.40   $100.40   $100.40  
  Purchase #5 $177.79   7.117%   $190.4433   $190.44   $190.45   $190.40  
  Purchase #6 $43.33   9.383%   $47.3957   $47.40   $47.40   $47.40  
  Purchase #7 $88.70   3.656%   $91.9429   $91.94   $91.95   $91.90  
  7 purchase totals = $999.55       $1,095.2474   $1,095.25   $1,095.25   $1,095.20