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 $47.27   6.444%   $50.3161   $50.32   $50.30   $50.30  
  Purchase #2 $220.51   9.806%   $242.1332   $242.13   $242.15   $242.10  
  Purchase #3 $157.33   4.583%   $164.5404   $164.54   $164.55   $164.50  
  Purchase #4 $206.99   13.225%   $234.3644   $234.36   $234.35   $234.40  
  Purchase #5 $156.28   10.526%   $172.73   $172.73   $172.75   $172.70  
  Purchase #6 $129.52   4.455%   $135.2901   $135.29   $135.30   $135.30  
  Purchase #7 $23.40   11.659%   $26.1282   $26.13   $26.15   $26.10  
  7 purchase totals = $941.30       $1,025.5024   $1,025.50   $1,025.55   $1,025.40