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 $147.87   11.548%   $164.946   $164.95   $164.95   $164.90  
  Purchase #2 $31.61   5.513%   $33.3527   $33.35   $33.35   $33.40  
  Purchase #3 $129.68   4.432%   $135.4274   $135.43   $135.45   $135.40  
  Purchase #4 $41.63   7.720%   $44.8438   $44.84   $44.85   $44.80  
  Purchase #5 $231.90   8.477%   $251.5582   $251.56   $251.55   $251.60  
  Purchase #6 $174.46   5.642%   $184.303   $184.30   $184.30   $184.30  
  Purchase #7 $207.71   11.773%   $232.1637   $232.16   $232.15   $232.20  
  7 purchase totals = $964.86       $1,046.5948   $1,046.59   $1,046.60   $1,046.60