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 $228.82   11.298%   $254.6721   $254.67   $254.65   $254.70  
  Purchase #2 $238.86   5.836%   $252.7999   $252.80   $252.80   $252.80  
  Purchase #3 $10.95   13.175%   $12.3927   $12.39   $12.40   $12.40  
  Purchase #4 $77.74   9.714%   $85.2917   $85.29   $85.30   $85.30  
  Purchase #5 $223.94   7.149%   $239.9495   $239.95   $239.95   $239.90  
  Purchase #6 $125.25   5.357%   $131.9596   $131.96   $131.95   $132.00  
  Purchase #7 $30.36   11.760%   $33.9303   $33.93   $33.95   $33.90  
  7 purchase totals = $935.92       $1,010.9958   $1,010.99   $1,011.00   $1,011.00