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 $84.83   10.553%   $93.7821   $93.78   $93.80   $93.80  
  Purchase #2 $91.56   11.551%   $102.1361   $102.14   $102.15   $102.10  
  Purchase #3 $82.97   12.672%   $93.484   $93.48   $93.50   $93.50  
  Purchase #4 $155.83   4.762%   $163.2506   $163.25   $163.25   $163.30  
  Purchase #5 $44.81   6.404%   $47.6796   $47.68   $47.70   $47.70  
  Purchase #6 $232.51   6.250%   $247.0419   $247.04   $247.05   $247.00  
  Purchase #7 $224.48   6.272%   $238.5594   $238.56   $238.55   $238.60  
  7 purchase totals = $916.99       $985.9337   $985.93   $986.00   $986.00