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 $35.77   6.568%   $38.1194   $38.12   $38.10   $38.10  
  Purchase #2 $235.58   12.672%   $265.4327   $265.43   $265.45   $265.40  
  Purchase #3 $202.87   9.284%   $221.7045   $221.70   $221.70   $221.70  
  Purchase #4 $80.59   4.225%   $83.9949   $83.99   $84.00   $84.00  
  Purchase #5 $192.25   9.498%   $210.5099   $210.51   $210.50   $210.50  
  Purchase #6 $162.63   13.405%   $184.4306   $184.43   $184.45   $184.40  
  Purchase #7 $143.87   9.647%   $157.7491   $157.75   $157.75   $157.70  
  7 purchase totals = $1,053.56       $1,161.9411   $1,161.93   $1,161.95   $1,161.80