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 $135.61   7.661%   $145.9991   $146.00   $146.00   $146.00  
  Purchase #2 $223.48   3.324%   $230.9085   $230.91   $230.90   $230.90  
  Purchase #3 $54.56   10.168%   $60.1077   $60.11   $60.10   $60.10  
  Purchase #4 $197.36   4.551%   $206.3419   $206.34   $206.35   $206.30  
  Purchase #5 $173.80   6.202%   $184.5791   $184.58   $184.60   $184.60  
  Purchase #6 $160.88   11.150%   $178.8181   $178.82   $178.80   $178.80  
  Purchase #7 $49.77   4.596%   $52.0574   $52.06   $52.05   $52.10  
  7 purchase totals = $995.46       $1,058.8118   $1,058.82   $1,058.80   $1,058.80