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 $109.87   11.751%   $122.7808   $122.78   $122.80   $122.80  
  Purchase #2 $242.45   5.161%   $254.9628   $254.96   $254.95   $255.00  
  Purchase #3 $68.58   10.843%   $76.0161   $76.02   $76.00   $76.00  
  Purchase #4 $151.73   9.653%   $166.3765   $166.38   $166.40   $166.40  
  Purchase #5 $243.84   3.742%   $252.9645   $252.96   $252.95   $253.00  
  Purchase #6 $187.80   3.127%   $193.6725   $193.67   $193.65   $193.70  
  Purchase #7 $56.70   4.242%   $59.1052   $59.11   $59.10   $59.10  
  7 purchase totals = $1,060.97       $1,125.8784   $1,125.88   $1,125.85   $1,126.00