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 $69.62   8.620%   $75.6212   $75.62   $75.60   $75.60  
  Purchase #2 $80.94   5.869%   $85.6904   $85.69   $85.70   $85.70  
  Purchase #3 $174.90   3.483%   $180.9918   $180.99   $181.00   $181.00  
  Purchase #4 $34.86   7.566%   $37.4975   $37.50   $37.50   $37.50  
  Purchase #5 $235.57   5.455%   $248.4203   $248.42   $248.40   $248.40  
  Purchase #6 $31.61   7.160%   $33.8733   $33.87   $33.85   $33.90  
  Purchase #7 $121.44   3.717%   $125.9539   $125.95   $125.95   $126.00  
  7 purchase totals = $748.94       $788.0484   $788.04   $788.00   $788.10