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 $24.62   13.550%   $27.956   $27.96   $27.95   $28.00  
  Purchase #2 $215.45   6.233%   $228.879   $228.88   $228.90   $228.90  
  Purchase #3 $109.91   9.569%   $120.4273   $120.43   $120.45   $120.40  
  Purchase #4 $150.38   11.336%   $167.4271   $167.43   $167.45   $167.40  
  Purchase #5 $54.41   5.641%   $57.4793   $57.48   $57.50   $57.50  
  Purchase #6 $173.92   9.651%   $190.705   $190.71   $190.70   $190.70  
  Purchase #7 $125.92   5.677%   $133.0685   $133.07   $133.05   $133.10  
  7 purchase totals = $854.61       $925.9422   $925.96   $926.00   $926.00