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 $165.70   7.381%   $177.9303   $177.93   $177.95   $177.90  
  Purchase #2 $72.43   7.615%   $77.9455   $77.95   $77.95   $77.90  
  Purchase #3 $127.80   4.843%   $133.9894   $133.99   $134.00   $134.00  
  Purchase #4 $42.32   9.554%   $46.3633   $46.36   $46.35   $46.40  
  Purchase #5 $235.84   13.182%   $266.9284   $266.93   $266.95   $266.90  
  Purchase #6 $236.53   10.774%   $262.0137   $262.01   $262.00   $262.00  
  Purchase #7 $246.46   11.344%   $274.4184   $274.42   $274.40   $274.40  
  7 purchase totals = $1,127.08       $1,239.5890   $1,239.59   $1,239.60   $1,239.50