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 $182.76   3.442%   $189.0506   $189.05   $189.05   $189.10  
  Purchase #2 $176.90   11.851%   $197.8644   $197.86   $197.85   $197.90  
  Purchase #3 $187.44   8.128%   $202.6751   $202.68   $202.70   $202.70  
  Purchase #4 $8.79   7.822%   $9.4776   $9.48   $9.50   $9.50  
  Purchase #5 $160.34   12.588%   $180.5236   $180.52   $180.50   $180.50  
  Purchase #6 $13.86   5.609%   $14.6374   $14.64   $14.65   $14.60  
  Purchase #7 $183.38   9.830%   $201.4063   $201.41   $201.40   $201.40  
  7 purchase totals = $913.47       $995.6350   $995.64   $995.65   $995.70