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 $23.68   12.794%   $26.7096   $26.71   $26.70   $26.70  
  Purchase #2 $182.43   11.274%   $202.9972   $203.00   $203.00   $203.00  
  Purchase #3 $208.55   5.353%   $219.7137   $219.71   $219.70   $219.70  
  Purchase #4 $182.44   5.847%   $193.1073   $193.11   $193.10   $193.10  
  Purchase #5 $125.28   10.499%   $138.4331   $138.43   $138.45   $138.40  
  Purchase #6 $96.26   12.211%   $108.0143   $108.01   $108.00   $108.00  
  Purchase #7 $140.83   11.435%   $156.9339   $156.93   $156.95   $156.90  
  7 purchase totals = $959.47       $1,045.9091   $1,045.90   $1,045.90   $1,045.80