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 $234.70   13.651%   $266.7389   $266.74   $266.75   $266.70  
  Purchase #2 $188.64   11.158%   $209.6885   $209.69   $209.70   $209.70  
  Purchase #3 $12.79   12.657%   $14.4088   $14.41   $14.40   $14.40  
  Purchase #4 $174.36   8.475%   $189.137   $189.14   $189.15   $189.10  
  Purchase #5 $23.25   9.198%   $25.3885   $25.39   $25.40   $25.40  
  Purchase #6 $238.46   5.156%   $250.755   $250.76   $250.75   $250.80  
  Purchase #7 $152.39   9.623%   $167.0545   $167.05   $167.05   $167.10  
  7 purchase totals = $1,024.59       $1,123.1712   $1,123.18   $1,123.20   $1,123.20