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 $126.73   6.519%   $134.9915   $134.99   $135.00   $135.00  
  Purchase #2 $55.93   11.795%   $62.5269   $62.53   $62.55   $62.50  
  Purchase #3 $66.68   3.405%   $68.9505   $68.95   $68.95   $69.00  
  Purchase #4 $120.85   4.378%   $126.1408   $126.14   $126.15   $126.10  
  Purchase #5 $227.32   11.755%   $254.0415   $254.04   $254.05   $254.00  
  Purchase #6 $197.66   6.665%   $210.834   $210.83   $210.85   $210.80  
  Purchase #7 $250.41   6.124%   $265.7451   $265.75   $265.75   $265.70  
  7 purchase totals = $1,045.58       $1,123.2303   $1,123.23   $1,123.30   $1,123.10