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 $75.44   5.498%   $79.5877   $79.59   $79.60   $79.60  
  Purchase #2 $59.32   3.859%   $61.6092   $61.61   $61.60   $61.60  
  Purchase #3 $116.79   7.465%   $125.5084   $125.51   $125.50   $125.50  
  Purchase #4 $211.25   5.206%   $222.2477   $222.25   $222.25   $222.20  
  Purchase #5 $191.68   9.479%   $209.8493   $209.85   $209.85   $209.80  
  Purchase #6 $8.60   12.435%   $9.6694   $9.67   $9.65   $9.70  
  Purchase #7 $62.46   8.131%   $67.5386   $67.54   $67.55   $67.50  
  7 purchase totals = $725.54       $776.0103   $776.02   $776.00   $775.90