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 $23.84   10.120%   $26.2526   $26.25   $26.25   $26.30  
  Purchase #2 $88.44   3.285%   $91.3453   $91.35   $91.35   $91.30  
  Purchase #3 $167.68   6.849%   $179.1644   $179.16   $179.15   $179.20  
  Purchase #4 $189.53   12.154%   $212.5655   $212.57   $212.55   $212.60  
  Purchase #5 $157.66   13.841%   $179.4817   $179.48   $179.50   $179.50  
  Purchase #6 $155.38   7.595%   $167.1811   $167.18   $167.20   $167.20  
  Purchase #7 $92.58   4.166%   $96.4369   $96.44   $96.45   $96.40  
  7 purchase totals = $875.11       $952.4275   $952.43   $952.45   $952.50