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 $236.94   11.182%   $263.4346   $263.43   $263.45   $263.40  
  Purchase #2 $76.42   10.698%   $84.5954   $84.60   $84.60   $84.60  
  Purchase #3 $78.45   8.373%   $85.0186   $85.02   $85.00   $85.00  
  Purchase #4 $219.58   8.363%   $237.9435   $237.94   $237.95   $237.90  
  Purchase #5 $13.41   8.321%   $14.5258   $14.53   $14.55   $14.50  
  Purchase #6 $106.43   3.166%   $109.7996   $109.80   $109.80   $109.80  
  Purchase #7 $243.93   5.230%   $256.6875   $256.69   $256.70   $256.70  
  7 purchase totals = $975.16       $1,052.0050   $1,052.01   $1,052.05   $1,051.90