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 $250.55   13.111%   $283.3996   $283.40   $283.40   $283.40  
  Purchase #2 $126.99   6.595%   $135.365   $135.37   $135.35   $135.40  
  Purchase #3 $56.79   12.548%   $63.916   $63.92   $63.90   $63.90  
  Purchase #4 $167.83   4.746%   $175.7952   $175.80   $175.80   $175.80  
  Purchase #5 $103.92   13.856%   $118.3192   $118.32   $118.30   $118.30  
  Purchase #6 $190.91   10.693%   $211.324   $211.32   $211.30   $211.30  
  Purchase #7 $197.77   4.775%   $207.2135   $207.21   $207.20   $207.20  
  7 purchase totals = $1,094.76       $1,195.3325   $1,195.34   $1,195.25   $1,195.30