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 $207.37   12.556%   $233.4074   $233.41   $233.40   $233.40  
  Purchase #2 $157.29   6.322%   $167.2339   $167.23   $167.25   $167.20  
  Purchase #3 $52.39   13.771%   $59.6046   $59.60   $59.60   $59.60  
  Purchase #4 $230.38   3.505%   $238.4548   $238.45   $238.45   $238.50  
  Purchase #5 $235.93   6.410%   $251.0531   $251.05   $251.05   $251.10  
  Purchase #6 $221.37   12.357%   $248.7247   $248.72   $248.70   $248.70  
  Purchase #7 $62.41   10.649%   $69.056   $69.06   $69.05   $69.10  
  7 purchase totals = $1,167.14       $1,267.5345   $1,267.52   $1,267.50   $1,267.60