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 $60.48   4.659%   $63.2978   $63.30   $63.30   $63.30  
  Purchase #2 $74.86   8.192%   $80.9925   $80.99   $81.00   $81.00  
  Purchase #3 $145.29   13.543%   $164.9666   $164.97   $164.95   $165.00  
  Purchase #4 $178.71   9.369%   $195.4533   $195.45   $195.45   $195.50  
  Purchase #5 $248.72   11.196%   $276.5667   $276.57   $276.55   $276.60  
  Purchase #6 $170.69   7.695%   $183.8246   $183.82   $183.80   $183.80  
  Purchase #7 $250.33   6.730%   $267.1772   $267.18   $267.20   $267.20  
  7 purchase totals = $1,129.08       $1,232.2787   $1,232.28   $1,232.25   $1,232.40