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 $67.38   10.272%   $74.3013   $74.30   $74.30   $74.30  
  Purchase #2 $32.44   3.740%   $33.6533   $33.65   $33.65   $33.70  
  Purchase #3 $40.70   13.471%   $46.1827   $46.18   $46.20   $46.20  
  Purchase #4 $165.56   11.698%   $184.9272   $184.93   $184.95   $184.90  
  Purchase #5 $134.28   7.200%   $143.9482   $143.95   $143.95   $143.90  
  Purchase #6 $28.60   7.644%   $30.7862   $30.79   $30.80   $30.80  
  Purchase #7 $167.68   6.519%   $178.6111   $178.61   $178.60   $178.60  
  7 purchase totals = $636.64       $692.4100   $692.41   $692.45   $692.40