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 $205.59   5.728%   $217.3662   $217.37   $217.35   $217.40  
  Purchase #2 $190.63   3.432%   $197.1724   $197.17   $197.15   $197.20  
  Purchase #3 $63.29   10.315%   $69.8184   $69.82   $69.80   $69.80  
  Purchase #4 $190.51   7.229%   $204.282   $204.28   $204.30   $204.30  
  Purchase #5 $207.56   12.762%   $234.0488   $234.05   $234.05   $234.00  
  Purchase #6 $65.87   5.442%   $69.4546   $69.45   $69.45   $69.50  
  Purchase #7 $52.48   7.433%   $56.3808   $56.38   $56.40   $56.40  
  7 purchase totals = $975.93       $1,048.5232   $1,048.52   $1,048.50   $1,048.60