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 $176.49   10.364%   $194.7814   $194.78   $194.80   $194.80  
  Purchase #2 $192.53   9.827%   $211.4499   $211.45   $211.45   $211.40  
  Purchase #3 $25.89   4.176%   $26.9712   $26.97   $26.95   $27.00  
  Purchase #4 $227.50   11.505%   $253.6739   $253.67   $253.65   $253.70  
  Purchase #5 $69.44   10.385%   $76.6513   $76.65   $76.65   $76.70  
  Purchase #6 $247.97   8.419%   $268.8466   $268.85   $268.85   $268.80  
  Purchase #7 $63.38   12.660%   $71.4039   $71.40   $71.40   $71.40  
  7 purchase totals = $1,003.20       $1,103.7782   $1,103.77   $1,103.75   $1,103.80