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 $217.52   8.272%   $235.5133   $235.51   $235.50   $235.50  
  Purchase #2 $89.40   3.139%   $92.2063   $92.21   $92.20   $92.20  
  Purchase #3 $245.92   12.696%   $277.142   $277.14   $277.15   $277.10  
  Purchase #4 $141.57   8.320%   $153.3486   $153.35   $153.35   $153.30  
  Purchase #5 $174.37   3.399%   $180.2968   $180.30   $180.30   $180.30  
  Purchase #6 $27.25   12.179%   $30.5688   $30.57   $30.55   $30.60  
  Purchase #7 $217.58   4.299%   $226.9338   $226.93   $226.95   $226.90  
  7 purchase totals = $1,113.61       $1,196.0096   $1,196.01   $1,196.00   $1,195.90