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 $30.83   13.690%   $35.0506   $35.05   $35.05   $35.10  
  Purchase #2 $61.45   13.108%   $69.5049   $69.50   $69.50   $69.50  
  Purchase #3 $199.42   6.670%   $212.7213   $212.72   $212.70   $212.70  
  Purchase #4 $224.32   12.656%   $252.7099   $252.71   $252.70   $252.70  
  Purchase #5 $167.37   13.150%   $189.3792   $189.38   $189.40   $189.40  
  Purchase #6 $204.58   11.790%   $228.7   $228.70   $228.70   $228.70  
  Purchase #7 $49.33   12.495%   $55.4938   $55.49   $55.50   $55.50  
  7 purchase totals = $937.30       $1,043.5597   $1,043.55   $1,043.55   $1,043.60