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 $32.64   9.127%   $35.6191   $35.62   $35.60   $35.60  
  Purchase #2 $223.41   12.283%   $250.8515   $250.85   $250.85   $250.90  
  Purchase #3 $23.65   4.214%   $24.6466   $24.65   $24.65   $24.60  
  Purchase #4 $197.62   9.459%   $216.3129   $216.31   $216.30   $216.30  
  Purchase #5 $161.83   13.504%   $183.6835   $183.68   $183.70   $183.70  
  Purchase #6 $186.36   6.474%   $198.4249   $198.42   $198.40   $198.40  
  Purchase #7 $83.98   11.531%   $93.6637   $93.66   $93.65   $93.70  
  7 purchase totals = $909.49       $1,003.2022   $1,003.19   $1,003.15   $1,003.20